U.S. patent number 7,586,060 [Application Number 10/584,825] was granted by the patent office on 2009-09-08 for protective sheet for laser processing and manufacturing method of laser processed parts.
This patent grant is currently assigned to Nitto Denko Corporation. Invention is credited to Atsushi Hino, Takeshi Matsumura, Naoyuki Matsuo, Tomokazu Takahashi, Masakatsu Urairi, Syouji Yamamoto.
United States Patent |
7,586,060 |
Urairi , et al. |
September 8, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Protective sheet for laser processing and manufacturing method of
laser processed parts
Abstract
A laser processing protection sheet (2) capable of effectively
preventing contamination on the surface of an article to be
processed by decomposition products when the article to be
processed (1) is processed by the UV absorption ablation of a laser
beam (7). A production method for a laser processed article (10)
using the laser processing protection sheet (2). The laser
processing protection sheet (2) is provided on the laser beam
incident surface side of the article to be processed (1) when the
article (1) is processed by the UV absorption ablation of the laser
beam (7).
Inventors: |
Urairi; Masakatsu (Ibaraki,
JP), Hino; Atsushi (Ibaraki, JP), Matsuo;
Naoyuki (Ibaraki, JP), Takahashi; Tomokazu
(Ibaraki, JP), Matsumura; Takeshi (Ibaraki,
JP), Yamamoto; Syouji (Ibaraki, JP) |
Assignee: |
Nitto Denko Corporation (Osaka,
JP)
|
Family
ID: |
34744036 |
Appl.
No.: |
10/584,825 |
Filed: |
November 2, 2004 |
PCT
Filed: |
November 02, 2004 |
PCT No.: |
PCT/JP2004/016268 |
371(c)(1),(2),(4) Date: |
June 26, 2006 |
PCT
Pub. No.: |
WO2005/063435 |
PCT
Pub. Date: |
July 14, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070181543 A1 |
Aug 9, 2007 |
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Foreign Application Priority Data
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Dec 25, 2003 [JP] |
|
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2003-430451 |
Dec 25, 2003 [JP] |
|
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2003-430463 |
Mar 30, 2004 [JP] |
|
|
2004-099896 |
Mar 30, 2004 [JP] |
|
|
2004-100112 |
Mar 30, 2004 [JP] |
|
|
2004-100127 |
Mar 30, 2004 [JP] |
|
|
2004-100141 |
Mar 30, 2004 [JP] |
|
|
2004-100199 |
Mar 30, 2004 [JP] |
|
|
2004-100281 |
|
Current U.S.
Class: |
219/121.71;
219/121.72 |
Current CPC
Class: |
B23K
26/40 (20130101); C09J 7/22 (20180101); B23K
26/18 (20130101); H05K 3/0026 (20130101); B23K
2103/50 (20180801); C09J 2483/006 (20130101); B23K
2101/40 (20180801); H05K 2203/1383 (20130101); Y10T
428/28 (20150115); C09J 2425/006 (20130101) |
Current International
Class: |
B23K
26/38 (20060101) |
Field of
Search: |
;219/121.7,121.71,121.72
;525/327.4 ;156/272.8 |
References Cited
[Referenced By]
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JP |
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JP |
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2005-279680 |
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JP |
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2005-279682 |
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JP |
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JP |
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JP |
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2005-279749 |
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JP |
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2005-279752 |
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Oct 2005 |
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JP |
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2005-279754 |
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Oct 2005 |
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JP |
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2005-279755 |
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Oct 2005 |
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JP |
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2005-279757 |
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Oct 2005 |
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JP |
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2005-279758 |
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Oct 2005 |
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JP |
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2006-192474 |
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2006-192478 |
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JP |
|
WO 01/41968 |
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Jun 2001 |
|
WO |
|
WO 2004/096483 |
|
Nov 2004 |
|
WO |
|
WO 2005/063435 |
|
Jul 2005 |
|
WO |
|
Other References
Chinese Office Action issued on the corresponding Chinese Patent
Application No. 200480038742.8, dated May 5, 2008. cited by other
.
International Search Report issued on the related PCT Application
No. PCT/JP2004/005554, dated Aug. 10, 2004. cited by other .
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Application No. PCT/JP2004/016268, dated Feb. 15, 2005. cited by
other .
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13, 2008. cited by other .
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Japanese Office Action issued on the corresponding Japanese Patent
Application No. 2003-430451, dated Jun. 24, 2009. cited by
other.
|
Primary Examiner: Evans; Geoffrey S
Attorney, Agent or Firm: Knobbe Martens Olson & Bear
LLP
Claims
The invention claimed is:
1. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with the density of the base material of
1.1 g/cm.sup.3 or more, comprising a step of adhering an adhesive
layer of the protective sheet for laser processing to the incident
side of laser beam of a workpiece, a step of processing the
protective sheet for laser processing and workpiece by irradiating
with laser beam, and a step of peeling off the protective sheet for
laser processing from the workpiece after processing, wherein said
base material comprises a base polymer and a filler, said filler
being selected from the group consisting of a colorant, a pigment,
a dye, gold, copper, platinum, silver, fine metal particles, metal
colloids, carbon particles, and inorganic particles, wherein said
filler is 2-20 parts by weight per 100 parts of the base polymer,
and wherein the workpiece is any one of sheet material, circuit
board, semiconductor wafer, metal substrate, semiconductor laser
light emitting or photo detecting element board, MEMS board, and
semiconductor package.
2. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with the density of the base material of
1.1 g/cm.sup.3 or more, comprising a step of adhering an adhesive
layer of the protective sheet for laser processing to the incident
side of laser beam of metal material, a step of processing the
protective sheet for laser processing and metal material by
irradiating with laser beam, and a step of peeling off the
protective sheet for laser processing from the metal material after
processing, wherein said base material comprises a base polymer and
a filler, said filler being selected from the group consisting of a
colorant, a pigment, a dye, gold, copper, platinum, silver, fine
metal particles, metal colloids, carbon particles, and inorganic
particles, and wherein said filler is 2-20 parts by weight per 100
parts of the base polymer.
3. The manufacturing method of claim 2, wherein the ratio of
extinction coefficient at ultraviolet region wavelength .lamda. of
the base material to extinction coefficient at ultraviolet region
wavelength .lamda. of metal material (extinction coefficient
ratio=extinction coefficient at ultraviolet region wavelength
.lamda. of base material of protective sheet for laser
processing/extinction coefficient at ultraviolet region wavelength
.lamda. of metal material) is 1 or more.
4. The manufacturing method of claim 2, wherein the extinction
coefficient at ultraviolet region wavelength .lamda. of the base
material is 20 cm.sup.-1 or more.
5. The manufacturing method of laser processed parts of claim 3 or
4, wherein the ultraviolet region wavelength .lamda. is 355 nm.
6. The manufacturing method of claim 2, wherein the ratio of
density of the base material to density of metal material (density
ratio=density of base material of protective sheet for laser
processing/density of metal material) is 1 or more.
7. The manufacturing method of claim 2, wherein the ratio of
tensile strength of protective sheet for laser processing to
tensile strength of metal material (tensile strength ratio=tensile
strength of protective sheet for laser processing/tensile strength
of metal material) is 1 or more.
8. The manufacturing method of claim 2, wherein the protective
sheet has a tensile strength of 100 MPa or more.
9. The manufacturing method of claim 2, wherein the specific heat
of the base material to specific heat of metal material (specific
heat ratio=specific heat of base material of protective sheet for
laser processing/specific heat of metal material) is less than
1.
10. The manufacturing method of laser process parts of claim 2,
wherein the base material contains aromatic polymer or silicone
rubber.
11. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with the density of the base material of
1.1 g/cm.sup.3 or more, comprising a step of adhering an adhesive
layer of the protective sheet for laser processing to the incident
side of laser beam of a workpiece, a step of processing the
protective sheet for laser processing and workpiece by irradiating
with laser beam, and a step of peeling off the protective sheet for
laser processing from the workpiece after processing, wherein said
base material comprises a base polymer and a filler, said filler
being selected from the group consisting of a colorant, a pigment,
a dye, gold, copper, platinum, silver, fine metal particles, metal
colloids, carbon particles, and inorganic particles, wherein said
filler is 2-20 parts by weight per 100 parts of the base polymer,
and wherein the workpiece is semiconductor wafer or metal
substrate.
12. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with 1 or more of ratio of refractive
index at wavelength 546 nm of the base material to refractive index
at wavelength 546 nm of organic workpiece (refractive index
ratio=refractive index at wavelength 546 nm of base material of
protective sheet for laser processing/refractive index at
wavelength 546 nm of organic workpiece), comprising a step of
adhering an adhesive layer of the protective sheet for laser
processing to the incident side of laser beam of the organic
workpiece, a step of processing the protective sheet for laser
processing and organic workpiece by irradiating with laser beam,
and a step of peeling off the protective sheet for laser processing
from the organic workpiece after processing, wherein said base
material comprises a base polymer and a filler, said filler being
selected from the group consisting of a colorant, a pigment, a dye,
gold, copper, platinum, silver, fine metal particles, metal
colloids, carbon particles, and inorganic particles, and wherein
said filler is 2-20 parts by weight per 100 parts of the base
polymer.
13. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with less than 1 of total coupling energy
ratio (total coupling energy ratio=total coupling energy A
equivalent to minimum value among sums of coupling energy of one
carbon atom in resin component for composing a base material and
other atom coupled with the carbon atom/total coupling energy B
equivalent to minimum value among sums of coupling energy of one
carbon atom in material component for composing an organic
workpiece and other atom coupled with the carbon atom, comprising a
step of adhering an adhesive layer of protective sheet for laser
processing to the incident side of laser beam of the organic
workpiece, a step of processing the protective sheet for laser
processing and organic workpiece by irradiating with laser beam,
and a step of peeling off the protective sheet for laser processing
from the organic workpiece after processing, wherein said base
material comprises a base polymer and a filler, said filler being
selected from the group consisting of a colorant, a pigment, a dye,
gold, copper, platinum, silver, fine metal particles, metal
colloids, carbon particles, and inorganic particles, and wherein
said filler is 2-20 parts by weight per 100 parts of the base
polymer.
14. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with refractive index at wavelength 546
nm of the base material of 1.53 or more, comprising a step of
adhering an adhesive layer of the protective sheet for laser
processing to the incident side of laser beam of inorganic
workpiece, a step of processing the protective sheet for laser
processing and inorganic workpiece by irradiating with laser beam,
and a step of peeling off the protective sheet for laser processing
from the inorganic workpiece after processing, wherein said base
material comprises a base polymer and a filler, said filler being
selected from the group consisting of a colorant, a pigment, a dye,
gold, copper, platinum, silver, fine metal particles, metal
colloids, carbon particles, and inorganic particles, and wherein
said filler is 2-20 parts by weight per 100 parts of the base
polymer.
15. A manufacturing method of laser processed parts by using a
protective sheet for laser processing having at least an adhesive
layer on a base material, with total coupling energy A equivalent
to minimum value among sums of coupling energy of one carbon atom
in resin component for composing a base material and other atom
coupled with the carbon atom of less than 800 kJ/mol, comprising a
step of adhering an adhesive layer of protective sheet for laser
processing to the incident side of laser beam of inorganic
workpiece, a step of processing the protective sheet for laser
processing and inorganic workpiece by irradiating with laser beam,
and a step of peeling off the protective sheet for laser processing
from the inorganic workpiece after processing, wherein said base
material comprises a base polymer and a filler, said filler being
selected from the group consisting of a colorant, a pigment, a dye,
gold, copper, platinum, silver, fine metal particles, metal
colloids, carbon particles, and inorganic particles, and wherein
said filler is 2-20 parts by weight per 100 parts of the base
polymer.
16. The manufacturing method of laser processed parts of claim 14
or 15, wherein the inorganic workpiece is any one of circuit board,
semiconductor wafer, glass substrate, ceramic substrate, metal
substrate, semiconductor laser light emitting or photo detecting
element board, MEMS board, and semiconductor package.
Description
This application is the U.S. National Phase under 35 U.S.C.
.sctn.371 of International Application PCT/JP2004/016268, filed
Nov. 2, 2004, which claims priority to Japanese Patent Application
No. 2003-430463, filed Dec. 25, 2003, Japanese Patent Application
No. 2003-430451, filed Dec. 25, 2003, Japanese Patent Application
No. 2004-100141, filed Mar. 30, 2004, Japanese Patent Application
No. 2004-100199, filed Mar. 30, 2004, Japanese Patent Application
No. 2004-100127, filed Mar. 30, 2004, Japanese Patent Application
No. 2004-099896, filed Mar. 30, 2004, Japanese Patent Application
No. 2004-100112, filed Mar. 30, 2004, and Japanese Patent
Application No. 2004-100281, filed Mar. 30, 2004. The International
Application was not published under PCT Article 21(2) in
English.
TECHNICAL FIELD
The present invention relates to a protective sheet for laser
processing used when processing a workpiece by ultraviolet
absorption ablation by laser beam. The invention also relates to a
manufacturing method of laser processed parts obtained by
processing workpieces such as sheet material, circuit board,
semiconductor wafer, glass substrate, ceramic substrate, metal
substrate, semiconductor laser or other light emitting and light
detecting element board, MEMS board, semiconductor package, cloth,
leather, paper or the like, by cutting, drilling, marking,
grooving, scribing, trimming or other shaping process by
ultraviolet absorption ablation by laser beam.
BACKGROUND ART
As the electronic and electric appliances are reduced in size
recently, component parts are also reduced in size and advanced in
definition, and high definition and high precision are demanded in
machining of parts at machining precision of +/-50 .mu.m or less.
In the conventional press processing or blanking process, the
precision is about +/-100 .mu.m at most, and such demand cannot be
satisfied. Drilling of materials is also demanded to conform to
high definition and high precision, and drilling by using
conventional drill or die cannot meet the needs.
To solve the problems, lately, machining of materials by using
laser beam is attracting wide attention. In particular, the
machining method by ultraviolet absorption ablation of laser beam
of small heat damage and high definition is noticed as precise
outline processing method or fine drilling method.
As the background art, for example, the dicing method of workpiece
includes a method of dicing the workpiece by laser beam while
supporting and fixing the workpiece on a dicing sheet (Japanese
Laid-open Patent No. 2002-343747). Also proposed is a method of
dicing a semiconductor wafer by combining laser with water micro
jet (Japanese Laid-open Patent No. 2003-34780). The dicing sheet
mentioned in these patent publications is disposed at the exit side
of laser beam of the workpiece, and is used for supporting and
fixing the workpiece (to be processed by laser) during dicing and
in the subsequent processes.
When laser beam is used, it requires aftertreatment called
desmearing in order to remove deposits of decomposition products of
carbon or the like generated by laser processing from the surface
of workpiece. The sticking strength of decomposition products is
firm in proportion to power of laser beam, and when the power of
laser beam is increased, it is difficult to remove deposits in
aftertreatment. In particular, at the side contacting with the
processing table of workpiece or adhesive sheet (the laser beam
exist side) is likely to be coated not only with the decomposition
products of workpiece but also with decomposition products of
processing table and adhesive sheet. As a result, improvement of
throughput of processing is impeded, or reliability of cutting or
drilling is lowered.
SUMMARY OF THE INVENTION
It is hence an object of the invention to present a protective
sheet for laser processing capable of effectively suppressing
contamination of workpiece surface by decomposition products when
processing the workpiece by ultraviolet absorption ablation of
laser beam. It is a further object of the invention to present a
manufacturing method of laser processed parts by using a protective
sheet for laser processing capable of effectively suppressing
contamination of workpiece surface by decomposition products when
processing the workpiece by ultraviolet absorption ablation of
laser beam, and also processing at high precision.
The present inventors have intensively accumulated studies in order
to solve the problems, and have completed the invention by
discovering that the objects can be achieved by using the following
protective sheet for laser processing (hereafter called protective
sheet) and the manufacturing method of laser processed parts by
using the protective sheet.
That is, a first aspect of the invention relates to a protective
sheet for laser processing disposed at the incident side of laser
beam of workpiece when processing the workpiece by ultraviolet
absorption ablation of laser beam.
The protective sheet is laminated at the incident side of laser
beam of workpiece (laser beam irradiation side) before laser
processing of workpiece by ultraviolet absorption ablation of laser
beam, and is used for protecting the workpiece surface from
decomposition products and scattering matter generated by ablation.
The protective sheet is processed together with the workpiece by
ultraviolet absorption ablation of laser beam. By using the
protective sheet, decomposition products generated from the laser
beam irradiation parts stick to the surface of the protective sheet
which covers the workpiece, and sticking of decomposition products
to the workpiece surface can be effectively prevented.
The light transmissivity of the protective sheet in the laser beam
absorption region is preferred to be less than 50%. By using the
protective sheet of which light transmissivity is less than 50%, it
is effective to prevent decomposition products from invading into
the interface of protective sheet and workpiece to stick to the
interface area. As a result, the protective sheet can be easily
peeled off from the workpiece after laser processing, and the laser
processing precision of workpiece can be enhanced at the same
time.
By using the protective sheet, contamination of interface area by
decomposition products can be suppressed, and its reason is
estimated as follows. When the light transmissivity of the
protective sheet in the laser beam absorption region is less than
50%, laser energy utilization efficiency of protective sheet is
great, and the protective sheet is eroded by the laser beam earlier
than the workpiece. After erosion of laser beam irradiation area of
protective sheet, its lower layer, that is, the workpiece is
eroded, but since decomposition products of workpiece are
effectively scattered outside from the eroded portions of the
protective sheet, contamination of interface area of the protective
sheet and workpiece can be suppressed.
More preferably, the light transmissivity of the protective sheet
in the laser beam absorption region should be less than 40%, and
further preferably less than 30%, and most preferably 0%. On the
other hand, when the light transmissivity is more than 50%, the
energy transmission increases to the workpiece which is a light
energy absorber, and erosion of workpiece by laser beam
transmitting through the protective sheet tends to be progressed
before the protective sheet is eroded by the laser beam. In such a
case, since there is no route of scattering for decomposition
products produced by erosion of workpiece, decomposition products
may invade into the space between the protective sheet and
workpiece, and the surface of workpiece may be contaminated. That
is, unless the protective sheet is ruptured or pierced by laser
ablation, since the gas pressure in decomposition of workpiece is
high, gaseous decomposition products are stagnant between the
protective sheet and workpiece, and such decomposition products
contaminate the workpiece surface. If the workpiece surface is
contaminated, it is hard to peel off the protective sheet from the
workpiece after laser processing of workpiece, and the processing
precision of workpiece tends to be lower.
The protective sheet is preferred to be provided with an adhesive
layer on a base material. When the protective sheet is provided
with adhesiveness, the contact tightness of the protective sheet
and workpiece is increased, and invasion of decomposition products
into the interface can be suppressed. As a result, contamination of
workpiece surface by decomposition products can be suppressed.
Also in the first aspect of the invention, the base material is
preferred to contain an aromatic polymer. By using an aromatic
polymer as forming material of base material, the light
transmissivity in the laser beam absorption region can be lowered,
and the etching speed of the protective sheet can be raised.
The ratio by weight of aromatic ring in repetition units for
composing the aromatic polymer is preferred to be 41 wt % or more,
and more preferably 50 wt % or more. If the ratio by weight of
aromatic ring is less than 41 wt %, the light transmissivity in the
laser beam absorption region cannot be lowered sufficiently, and it
tends to be difficult to enhance the etching speed of protective
sheet sufficiently.
A second aspect of the invention relates to a protective sheet for
laser processing used when processing the workpiece by ultraviolet
absorption ablation of laser beam, in which the protective sheet is
provided at least with an adhesive layer on the base material, and
the etching rate of the base material (etching speed/energy
fluence) is 0.4 [(.mu.m/pulse)/(J/cm.sup.2)] or more.
The etching rate calculated by dividing the etching speed
(.mu.m/pulse) of the base material by the energy fluence
(J/cm.sup.2) of the laser shows the degree of laser processability
of base material, and when the etching rate is higher, it is easier
to etch. The calculating method of the etching rate is specifically
described in the embodiment.
In the second aspect of the invention, by using the protective
sheet of which etching rate of base material is 0.4 or more,
contamination of workpiece surface by decomposition products can be
suppressed effectively. Its reason is estimated as follows. When
the etching rate of base material is more than 0.4, since the laser
energy utilization efficiency of base material is great, the base
material is etched by the laser beam earlier than the workpiece.
After etching of the laser beam irradiation part of protective
sheet, the workpiece in the lower layer is etched, but since the
decomposition products of workpiece effectively scatter about to
outside from the etching area of the protective sheet, they hardly
invade into the interface of protective sheet and workpiece, so
that contamination of workpiece surface can be suppressed.
The etching rate of the base material is preferred to be 0.5 or
more, or more preferably 0.6 or more. If the etching rate is less
than 0.4, the energy transmission increases to the workpiece which
is a light energy absorber, and etching of workpiece by laser beam
transmitting through the protective sheet is progressed before the
base material is sufficiently etched by the laser beam. In such a
case, since there is no route of scattering for decomposition
products produced by etching of workpiece, decomposition products
may invade into the interface area between the protective sheet and
workpiece, and the surface of workpiece may be contaminated. When
the workpiece surface is contaminated by decomposition products, as
mentioned above, it is hard to peel off the protective sheet from
the workpiece after laser processing of workpiece, and it is hard
to remove decomposition products in aftertreatment, and the
processing precision of workpiece tends to be lower.
The protective sheet is preferred to be provided with an adhesive
layer at least on a base material. When the protective sheet is
provided with adhesiveness, the contact tightness at the interface
of the protective sheet and workpiece is increased, and invasion of
decomposition products into the interface can be suppressed, and as
a result, contamination of workpiece surface by decomposition
products can be suppressed.
Also in the second aspect of the invention, the base material is
preferred to contain an aromatic polymer or silicone rubber. By
using an aromatic polymer or silicone rubber as forming material of
base material, it is easier to adjust the etching rate of base
material to 0.4 or more.
The invention also relates to a manufacturing method of laser
processed parts comprising a step of disposing a protective sheet
for laser processing at the incident side of laser beam of a
workpiece (1), a step of processing the protective sheet for laser
processing and the workpiece by irradiating with laser beam (2),
and a step of peeling the protective sheet for laser processing
from the workpiece after processing (3).
The workpiece is preferably any one of sheet material, circuit
board, semiconductor wafer, glass substrate, ceramic substrate,
metal substrate, semiconductor laser light emitting or light
detecting element board, MEMS board, and semiconductor package. The
processing is cutting or drilling process of workpiece.
The protective sheet of the invention is preferably used in
manufacture of semiconductor chip, especially, by dicing a
semiconductor wafer.
A third aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with 1 or more of ratio of extinction coefficient at ultraviolet
region wavelength .lamda. of base material to extinction
coefficient at ultraviolet region wavelength .lamda. of workpiece
(extinction coefficient ratio=extinction coefficient at ultraviolet
region wavelength .lamda. of base material of protective sheet for
laser processing/extinction coefficient at ultraviolet region
wavelength .lamda. of workpiece), comprising a step of adhering an
adhesive layer of protective sheet for laser processing to the
incident side of laser beam of workpiece, a step of processing the
protective sheet for laser processing and workpiece by irradiating
with laser beam, and a step of peeling off the protective sheet for
laser processing from the workpiece after processing.
In the manufacturing method of the third aspect of the invention,
it is important to select and use the protective sheet of which
ratio of extinction coefficient at ultraviolet region wavelength
.lamda. of base material to extinction coefficient at ultraviolet
region wavelength .lamda. of workpiece (extinction coefficient
ratio=extinction coefficient at ultraviolet region wavelength
.lamda. of base material of protective sheet for laser
processing/extinction coefficient at ultraviolet region wavelength
.lamda. of workpiece) is 1 or more. The inventors discovered a
correlation between the extinction coefficient and laser
processability, and found that contamination of workpiece surface
by decomposition products can be effectively suppressed by using a
protective sheet with the extinction coefficient ratio of 1 or
more. The ultraviolet region wavelength .lamda. is preferred to be
355 nm.
The extinction coefficient is an important parameter in relation to
the laser processability of base material of protective sheet and
workpiece. When the extinction coefficient of a solid matter at a
certain wavelength is smaller, the absorption of light energy is
smaller. That is, light absorption in a solid matter occurs at
light invasion length (effective distance from solid matter
surface: 1/extinction coefficient), and when the extinction
coefficient is small, the light invasion length is longer, and
hence the accumulated energy per volume is decreased. As a result,
laser processing is difficult in a material of small extinction
coefficient.
As in the third aspect of the invention, by using the protective
sheet of which extinction coefficient ratio is 1 or more, the laser
beam invasion length in the base material is set shorter than the
laser beam invasion length in the workpiece. Hence, the absorption
of light energy is greater in the base material than in the
workpiece, so that laser processing is easier.
By using the protective sheet of which extinction coefficient ratio
is 1 or more, contamination of workpiece surface by decomposition
products can be effectively suppressed, and its reason may be
estimated as follows. The protective sheet of which extinction
coefficient ratio is 1 or more is equivalent or superior in laser
processability to the workpiece, and it is etched by laser beam at
the same time as or earlier than the workpiece. Accordingly, the
decomposition products of workpiece are effectively scattered to
outside from the etching portion of the protective sheet, and
hardly invade into the interface of protective sheet and workpiece.
As a result, contamination of workpiece surface can be suppressed
effectively.
The extinction coefficient ratio is preferred to be 1.5 or more, or
more preferably 2 or more. If the extinction coefficient ratio is
less than 1, etching of workpiece is advanced before the protective
sheet is cut or pierced. In such a case, there is no route of
scattering for decomposition products produced by etching of
workpiece, and the decomposition products may invade into the
interface area of protective sheet and workpiece, and the workpiece
surface may be contaminated. If the workpiece surface is thus
contaminated by decomposition products, after laser processing of
workpiece, it is hard to peel off the protective sheet from the
workpiece, or it is hard to remove decomposition products in
aftertreatment, and the processing precision of workpiece tends to
be lower.
The base material is preferred to contain an aromatic polymer or
silicone rubber. Since this material is large in the extinction
coefficient at ultraviolet region wavelength .lamda., the
extinction coefficient ratio can be adjusted to 1 or more
relatively easily.
A fourth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with the extinction coefficient at ultraviolet region wavelength
.lamda. of base material of 20 cm.sup.-1 or more, comprising a step
of adhering an adhesive layer of protective sheet for laser
processing to the incident side of laser beam of metal material, a
step of processing the protective sheet for laser processing and
metal material by irradiating with laser beam, and a step of
peeling off the protective sheet for laser processing from the
metal material after processing.
In particular, when processing a metal material, it is difficult to
measure the extinction coefficient of metal material. However, by
controlling the extinction coefficient at ultraviolet region
wavelength .lamda. of base material of protective sheet at 20
cm.sup.-1 or more, contamination of surface of metal material by
decomposition products could be suppressed effectively. The
extinction coefficient at ultraviolet region wavelength .lamda. of
base material is preferred to be 50 cm.sup.-1 or more, or more
preferably 80 cm.sup.-1 or more. The ultraviolet region wavelength
.lamda. is preferred to be 355 nm.
A fifth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with 1 or more of ratio of density of base material to density of
workpiece (density ratio=density of base material of protective
sheet for laser processing/density of workpiece), comprising a step
of adhering an adhesive layer of protective sheet for laser
processing to the incident side of laser beam of workpiece, a step
of processing the protective sheet for laser processing and
workpiece by irradiating with laser beam, and a step of peeling off
the protective sheet for laser processing from the workpiece after
processing.
In the manufacturing method of the fifth aspect of the invention,
it is important to select and use the protective sheet of which
ratio of density of base material to ratio of workpiece (density
ratio=density of base material of protective sheet for laser
processing/radio of workpiece) or 1 or more. The inventors
discovered a correlation between the material density and laser
processability, and found that the higher density is preferred
because ablation is more likely to occur and laser processability
is higher. By selecting and using the protective sheet of which
density ratio is 1 or more, it is found more effective to suppress
contamination of workpiece surface by decomposition products. The
reason of correlation between density and laser processability is
not clear, but the material of large density is high in filling
rate of atoms, and the probability of laser beam colliding against
atoms per unit area of irradiation seems to be higher. Ultraviolet
ablation of laser beam is a phenomenon of a substance absorbing
photons to excite electrons, thereby segmenting coupling between
atoms. It is hence considered that laser processing is easier when
the photon absorption sectional area of laser beam is wider (that
is, the density is larger).
By selecting and using the protective sheet of which density ratio
is 1 or more, contamination of workpiece surface by decomposition
products can be suppressed effectively, and its reason is estimated
as follows. The protective sheet with density ratio of 1 or more is
equivalent or superior in laser processability to workpiece, and is
etched by laser beam at the same time as or earlier than the
workpiece. Hence, decomposition products of workpiece scatter
effectively to outside from the etching portion of the protective
sheet, and hardly invade into the interface of the protective sheet
and workpiece. As a result, contamination of workpiece surface can
be suppressed effectively.
The density ratio is preferred to be 1.1 or more, or more
preferably 1.4 or more. If the density ratio is less than 1,
etching of workpiece is advanced before the protective sheet is cut
or pierced. In such a case, there is no route of scattering for
decomposition products produced by etching of workpiece, and the
decomposition products may invade into the interface area of
protective sheet and workpiece, and the workpiece surface may be
contaminated. If the workpiece surface is thus contaminated by
decomposition products, after laser processing of workpiece, it is
hard to peel off the protective sheet from the workpiece, or it is
hard to remove decomposition products in aftertreatment, and the
processing precision of workpiece tends to be lower.
The base material of the protective sheet is preferred to contain
an aromatic polymer or silicone rubber from the viewpoint of high
density.
A sixth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with the density of base material of 1.1 g/cm.sup.3 or more,
comprising a step of adhering an adhesive layer of protective sheet
for laser processing to the incident side of laser beam of metal
material, a step of processing the protective sheet for laser
processing and metal material by irradiating with laser beam, and a
step of peeling off the protective sheet for laser processing from
the metal material after processing.
In particular, in laser processing of metal material, if the
density ratio is more than 1, etching of metal material may be
advanced before the protective sheet is cut or pierced. In such a
case, there is no route of scattering for decomposition products
produced by etching of metal material, and the decomposition
products may invade into the interface area of protective sheet and
metal material, and the surface of metal material may be
contaminated. As the cause of such phenomenon, difference in
ablation process between macromolecular material and metal material
may be considered. That is, the metal material undergoes a
thermochemical reactive process derived from the heat generated by
injection of light energy. Accordingly, the process efficiency of
macromolecular material and process efficiency of metal material
cannot be compared simply.
The inventors have comparatively studied between the processing
rate of metal material such as silicon and processing rate of
protective sheet, and found that the base material having the
density of 1.1 g/cm.sup.3 or more has a laser processability
equivalent to that of metal material and can effectively suppress
the contamination of surface of metal material by decomposition
products. More preferably, the density of the base material should
be 1.3 g/cm.sup.3 or more, or most preferably 1.5 g/cm.sup.3 or
more.
The base material of the protective sheet is preferred to contain
an aromatic polymer or silicone rubber from the viewpoint of high
density.
A seventh aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with 1 or more of ratio of tensile strength of protective sheet for
laser processing to tensile strength of workpiece (tensile strength
ratio=tensile strength of protective sheet for laser
processing/tensile strength of workpiece), comprising a step of
adhering an adhesive layer of protective sheet for laser processing
to the incident side of laser beam of workpiece, a step of
processing the protective sheet for laser processing and workpiece
by irradiating with laser beam, and a step of peeling off the
protective sheet for laser processing from the workpiece after
processing.
In the seventh aspect of the invention, it is important to select
and use the protective sheet of which ratio of tensile strength of
protective sheet to tensile strength of workpiece (tensile strength
ratio=tensile strength of protective sheet for laser
processing/tensile strength of workpiece) is 1 or more. The
inventors discovered a correlation between the tensile strength,
one of the mechanical properties, and the laser processability, and
found that contamination of workpiece surface by decomposition
products can be suppressed effectively by selecting and using the
protective sheet of which tensile strength ratio is 1 or more. The
reason of correlation between tensile strength and laser
processability is not clear, but a material of high tensile
strength often has aromatic or linear structure generally, and
molecules having such rigid structure are strong in the
intermolecular force by electrons of mutual cyclic atoms or hetero
atoms and are hence arrayed. As a result, collision probability is
high between atoms absorbing laser energy, and it is considered
that laser processability may be enhanced.
Therefore, by selecting and using the protective sheet of which
tensile strength ratio is 1 or more, contamination of workpiece
surface by decomposition products can be suppressed effectively,
and its reason is estimated as follows. The protective sheet of
which tensile strength ratio is 1 or more is equivalent or superior
in laser processability to workpiece, and is hence etched by laser
beam at the same time as or earlier than the workpiece. As a
result, decomposition products of workpiece efficiently scatter
about to outside from the etching portion of the protective sheet,
and hardly invade into the interface of protective sheet and
workpiece. Hence, contamination of workpiece surface can be
suppressed effectively.
The tensile strength ratio is preferred to be 2 or more, or more
preferably 5 or more. If the tensile strength ratio is less than 1,
the workpiece is etched before the protective sheet is cut or
pierced. In such a case, there is no route of scattering for
decomposition products produced by etching of workpiece, and
decomposition products invade into the interface of the protective
sheet and workpiece, possibly contaminating the workpiece surface.
If the workpiece surface is contaminated by decomposition products,
after laser processing of workpiece, it is hard to peel off the
protective sheet from the workpiece, or it is difficult to remove
decomposition products in aftertreatment, and the processing
precision of workpiece tends to drop.
An eighth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with the tensile strength of 100 MPa or more, comprising a step of
adhering an adhesive layer of protective sheet for laser processing
to the incident side of laser beam of metal material, a step of
processing the protective sheet for laser processing and metal
material by irradiating with laser beam, and a step of peeling off
the protective sheet for laser processing from the metal material
after processing.
In particular, in laser processing of metal material, if the
tensile strength ratio is more than 1, etching of metal material
may be advanced before the protective sheet is cut or pierced. In
such a case, there is no route of scattering for decomposition
products produced by etching of metal material, and the
decomposition products may invade into the interface area of
protective sheet and metal material, and the surface of metal
material may be contaminated. As the cause of such phenomenon,
difference in ablation process between macromolecular material and
metal material may be considered. That is, the metal material
undergoes a thermochemical reactive process derived from the heat
generated by injection of light energy. Accordingly, the process
efficiency of macromolecular material and process efficiency of
metal material cannot be compared simply.
The inventors have comparatively studied between the processing
rate of metal material such as silicon and processing rate of
protective sheet, and found that the protective sheet having a
tensile strength of 100 MPa or more has a laser processability
equivalent to that of metal material and can effectively suppress
the contamination of surface of metal material by decomposition
products. More preferably, the tensile strength of protective sheet
should be 120 MPa or more, more preferably 140 MPa or more, and
most preferably 200 MPa.
A ninth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with less than 1 of ratio of specific heat of base material to
specific heat of workpiece (specific heat ratio=specific heat of
base material of protective sheet for laser processing/specific
heat of workpiece), comprising a step of adhering an adhesive layer
of protective sheet for laser processing to the incident side of
laser beam of workpiece, a step of processing the protective sheet
for laser processing and workpiece by irradiating with laser beam,
and a step of peeling off the protective sheet for laser processing
from the workpiece after processing.
In the ninth aspect of the invention, it is important to select and
use the protective sheet of which ratio of specific heat of base
material to specific heat of workpiece (specific heat
ratio=specific heat of base material of protective sheet for laser
processing/specific heat of workpiece) of less than 1. The
inventors discovered a correlation between the specific heat of
material and the laser processability, and found that ablation is
more likely to occur at smaller specific heat, so that laser
processability is higher. That is, contamination of workpiece
surface by decomposition products can be suppressed effectively by
selecting and using the protective sheet of which specific heat
ratio is less than 1. The reason of correlation between specific
heat and laser processability is not clear, but ablation is
considered to take place by a mechanism of inducing a Coulomb
explosion as photons excite electrons in the material and a
mechanism of decomposing the material thermally. When the specific
heat of material is small, heat is absorbed and the temperature is
likely to rise, and laser processability seems to be higher.
Further, by selecting and using the protective sheet of which
specific heat ratio is less than 1, contamination of workpiece
surface by decomposition products can be suppressed effectively,
and its reason is estimated as follows. The protective sheet of
which specific heat ratio is less than 1 is equivalent or superior
in laser processability to workpiece, and is hence etched by laser
beam at the same time as or earlier than the workpiece. As a
result, decomposition products of workpiece efficiently scatter
about to outside from the etching portion of the protective sheet,
and hardly invade into the interface of protective sheet and
workpiece. Hence, contamination of workpiece surface can be
suppressed effectively.
The specific heat ratio is preferred to be 0.9 or less, or more
preferably 0.8 or less. If the specific heat ratio is more than 1,
the workpiece is etched before the protective sheet is cut or
pierced. In such a case, there is no route of scattering for
decomposition products produced by etching of workpiece, and
decomposition products invade into the interface of the protective
sheet and workpiece, possibly contaminating the workpiece surface.
If the workpiece surface is contaminated by decomposition products,
after laser processing of workpiece, it is hard to peel off the
protective sheet from the workpiece, or it is difficult to remove
decomposition products in aftertreatment, and the processing
precision of workpiece tends to drop.
In the manufacturing method of laser processed parts of the
invention in the third, fifth, seventh and ninth aspects, the
workpiece is preferred to be any one of sheet material, circuit
board, semiconductor wafer, glass substrate, ceramic substrate,
metal substrate, semiconductor laser light emitting or light
detecting element board, MEMS board, and semiconductor package.
In the manufacturing method of laser processed parts of the
invention in the fourth, sixth and eighth aspects, the metal
material is preferred to be semiconductor wafer or metal
substrate.
A tenth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with 1 or more of ratio of refractive index at wavelength 546 nm of
base material to refractive index at wavelength 546 nm of organic
workpiece (refractive index ratio=refractive index at wavelength
546 nm of base material of protective sheet for laser
processing/refractive index at wavelength 546 nm of organic
workpiece), comprising a step of adhering an adhesive layer of
protective sheet for laser processing to the incident side of laser
beam of organic workpiece, a step of processing the protective
sheet for laser processing and organic workpiece by irradiating
with laser beam, and a step of peeling off the protective sheet for
laser processing from the organic workpiece after processing.
In the tenth aspect of the invention, it is important to select and
use the protective sheet of which ratio of refractive index at
wavelength 546 nm of base material to refractive index at
wavelength 546 nm of organic workpiece (refractive index
ratio=refractive index at wavelength 546 nm of base material of
protective sheet for laser processing/refractive index at
wavelength 546 nm of organic workpiece) is 1 or more. The inventors
discovered a correlation between the refractive index and the laser
processability, and found that contamination of surface of organic
workpiece by decomposition products can be suppressed effectively
by selecting and using the protective sheet of which refractive
index ratio is more than 1.
The refractive index ratio is an important parameter for laser
processability of base material of protective sheet and organic
workpiece. The higher the refractive index of a solid matter at a
certain wavelength, the slower is the speed of light propagating
through the solid matter, and the probability of photo absorption
is higher. Mechanism of occurrence of laser ablation is derived
from electron excitation by photon absorption, and the laser
processability is considered to be higher when the speed of light
propagating in the solid matter is slower (that is, the refractive
index is larger).
In the invention, by using the protective sheet of which refractive
index ratio is 1 or more, photon absorption in the base material is
greater than in the organic workpiece, and the base material is
more likely to be processed by laser.
Further, by selecting and using the protective sheet of which
refractive index ratio is more than 1, contamination of surface of
organic workpiece by decomposition products can be suppressed
effectively, and its reason is estimated as follows. The protective
sheet of which refractive index ratio is more than 1 is equivalent
or superior in laser processability to organic workpiece, and is
hence etched by laser beam at the same time as or earlier than the
organic workpiece. As a result, decomposition products of organic
workpiece efficiently scatter about to outside from the etching
portion of the protective sheet, and hardly invade into the
interface of protective sheet and organic workpiece. Hence,
contamination of surface of organic workpiece can be suppressed
effectively.
The refractive index ratio is preferred to be more than 1.05, or
more preferably more than 1.1, and most preferable more than 1.2.
If the refractive index ratio is less than 1, the organic workpiece
is etched before the protective sheet is cut or pierced. In such a
case, there is no route of scattering for decomposition products
produced by etching of organic workpiece, and decomposition
products invade into the interface of the protective sheet and
organic workpiece, possibly contaminating the surface of organic
workpiece. If the surface of organic workpiece is contaminated by
decomposition products, after laser processing of organic
workpiece, it is hard to peel off the protective sheet from the
organic workpiece, or it is difficult to remove decomposition
products in aftertreatment, and the processing precision of organic
workpiece tends to drop.
An eleventh aspect of the invention relates to a manufacturing
method of laser processed parts by using a protective sheet for
laser processing having at least an adhesive layer on a base
material, with refractive index at wavelength 546 nm of base
material of 1.53 or more, comprising a step of adhering an adhesive
layer of protective sheet for laser processing to the incident side
of laser beam of inorganic workpiece, a step of processing the
protective sheet for laser processing and inorganic workpiece by
irradiating with laser beam, and a step of peeling off the
protective sheet for laser processing from the inorganic workpiece
after processing.
In the invention, the inorganic workpiece is preferred to be any
one of circuit board, semiconductor wafer, glass substrate, ceramic
substrate, metal substrate, semiconductor laser light emitting or
light detecting element board, MEMS board, and semiconductor
package.
When using the inorganic workpiece, it is hard to measure its
refractive index, but by defining the refractive index of base
material of protective sheet at 1.53 or more, contamination of
surface of inorganic workpiece by decomposition products can be
effectively suppressed. The refractive index of base material is
preferred to be 1.57 or more, or more preferably 1.60 or more.
In the invention, the base material of protective sheet is
preferred to contain an aromatic polymer or silicone rubber. Since
this material is large in refractive index at wavelength 546 nm,
the refractive index ratio can be adjusted to more than 1
relatively easily.
A twelfth aspect of the invention relates to a manufacturing method
of laser processed parts by using a protective sheet for laser
processing having at least an adhesive layer on a base material,
with less than 1 of ratio of total coupling energy ratio (total
coupling energy ratio=total coupling energy A equivalent to minimum
value among sums of coupling energy of one carbon atom in resin
component for composing a base material and other atom coupled with
the carbon atom/total coupling energy B equivalent to minimum value
among sums of coupling energy of one carbon atom in material
component for composing an organic workpiece and other atom coupled
with the carbon atom), comprising a step of adhering an adhesive
layer of protective sheet for laser processing to the incident side
of laser beam of organic workpiece, a step of processing the
protective sheet for laser processing and organic workpiece by
irradiating with laser beam, and a step of peeling off the
protective sheet for laser processing from the organic workpiece
after processing.
In the manufacturing method of the twelfth aspect of the invention,
it is important to select and use the protective sheet of which
total coupling energy ratio is less than 1.
Herein, the total coupling energy A is the smallest value among
sums of coupling energies (total coupling energy) of one carbon
atom in resin component for composing a base material and other
atom coupled with the carbon atom. A certain carbon atom in polymer
is coupled with two or more other atoms, and the coupling energy
varies with the kind of other atom being coupled, and hence the sum
of coupling energies (total coupling energy) also differs with the
coupling state of each carbon atom. In the invention, paying
attention to the carbon atom of lowest total coupling energy among
carbon atoms in various coupled states in the polymer, it is found
that the total coupling energy A of the carbon atom has a
correlation with the laser processability.
The total coupling energy B is the smallest value among sums of
coupling energies (total coupling energy) of one carbon atom in
material component for composing an organic workpiece and other
atom coupled with the carbon atom. In the invention, paying
attention to the carbon atom of lowest total coupling energy among
carbon atoms in various coupled states in the material component,
it is found that the total coupling energy B of the carbon atom has
a correlation with the laser processability.
The authors have discovered that contamination of surface of
organic workpiece by decomposition products can be effectively
suppressed by selecting and using a protective sheet of which total
coupling energy ratio is less than 1. The reason of such
correlation between total coupling energy and laser processability
is not clear, but the bond of atoms with small coupling energy is
likely to be broken with irradiated with laser, and the threshold
of processing drops. It is hence considered that the laser
processability is higher when the total coupling energy is smaller
between specific atoms in the material.
Further, by selecting and using the protective sheet of which total
coupling energy ratio is less than 1, contamination of surface of
organic workpiece by decomposition products can be suppressed
effectively, and its reason is estimated as follows. The protective
sheet of which total coupling energy ratio is less than 1 is
equivalent or superior in laser processability to organic
workpiece, and is hence etched by laser beam at the same time as or
earlier than the organic workpiece. As a result, decomposition
products of organic workpiece efficiently scatter about to outside
from the etching portion of the protective sheet, and hardly invade
into the interface of protective sheet and organic workpiece.
Hence, contamination of surface of organic workpiece can be
suppressed effectively.
The total coupling energy ratio is preferred to be 0.9 or less, or
more preferably 0.8 or less. If the total coupling energy ratio is
more than 1, the organic workpiece is etched before the protective
sheet is cut or pierced. In such a case, there is no route of
scattering for decomposition products produced by etching of
organic workpiece, and decomposition products invade into the
interface of the protective sheet and organic workpiece, possibly
contaminating the surface of organic workpiece. If the surface of
organic workpiece is contaminated by decomposition products, after
laser processing of organic workpiece, it is hard to peel off the
protective sheet from the organic workpiece, or it is difficult to
remove decomposition products in aftertreatment, and the processing
precision of organic workpiece tends to drop.
A thirteenth aspect of the invention relates to a manufacturing
method of laser processed parts by using a protective sheet for
laser processing having at least an adhesive layer on a base
material, with total coupling energy A equivalent to minimum value
among sums of coupling energy of one carbon atom in resin component
for composing a base material and other atom coupled with the
carbon atom of less than 800 kJ/mol, comprising a step of adhering
an adhesive layer of protective sheet for laser processing to the
incident side of laser beam of inorganic workpiece, a step of
processing the protective sheet for laser processing and inorganic
workpiece by irradiating with laser beam, and a step of peeling off
the protective sheet for laser processing from the inorganic
workpiece after processing.
In the invention, the inorganic workpiece is preferred to be any
one of circuit board, semiconductor wafer, glass substrate, ceramic
substrate, metal substrate, semiconductor laser light emitting or
light detecting element board, MEMS board, and semiconductor
package.
When using the inorganic workpiece, there is a thermochemical
reactive process derived from heat generated by injection of light
energy. That is, the ablation process varies significantly between
inorganic workpiece and organic workpiece. Hence, processing
efficiency of organic workpiece and processing efficiency of
inorganic workpiece cannot be compared simply.
The inventors have comparatively studied the processing rate of
inorganic workpiece and processing rate of organic workpiece, and
discovered that contamination of surface of inorganic workpiece by
decomposition products can be effectively suppressed by using the
protective sheet having a base material of which total coupling
energy A is less than 800 kJ/mol because it has a laser
processability equivalent or superior to that of inorganic
workpiece. The total coupling energy A is preferred to be 780
kJ/mol or less, or more preferably 760 kJ/mol or less.
In the third to thirteenth aspects of the invention, the protective
sheet is laminated at the incident side of laser beam of workpiece
(laser beam incident side) before laser processing of workpiece by
ultraviolet absorption ablation of laser beam, and is used for
protecting the surface of the workpiece from decomposition products
or scattering matter generated by ablation.
As the protective sheet, one having at least an adhesive layer on a
base material is used. By providing the protective sheet with
adhesiveness, the contact tightness with the interface of
protective sheet and workpiece is improved, and invasion of
decomposition products into interface can be suppressed, so that
contamination of surface of workpiece by decomposition products can
be suppressed.
In the third to thirteenth aspects of the invention, the base
material is preferred to contain an aromatic polymer or silicone
rubber.
In the third to thirteenth aspects of the invention, the processing
is cutting or drilling.
The invention relates to the protective sheet for laser processing
used in manufacturing method of laser processed parts. The
protective sheet is preferably used when manufacturing
semiconductor chips, in particular, by dicing a semiconductor
wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic process diagram showing an example of
manufacturing method of laser processed parts according to the
invention.
FIG. 2 is a schematic process diagram showing other example of
manufacturing method of laser processed parts according to the
invention.
FIG. 3 is a schematic diagram showing a section of a laminated body
processed by ultraviolet absorption ablation of laser beam.
FIG. 4 is a schematic diagram showing an example of dicing method
of semiconductor wafer.
BEST MODE FOR CARRYING OUT THE INVENTION
The laser used in the invention is the laser applicable in ablation
process by ultraviolet absorption, which is non-thermal process
without heating process, in order not to worsen the precision and
appearance of hole edge and cut section wall of workpiece due to
thermal damage during laser processing. In particular, it is
preferred to use the laser capable of focusing the laser beam into
a narrow width of 20 .lamda.m or less and emitting ultraviolet rays
of 400 nm or less.
In particular, the laser used in the third and fourth aspects of
the invention is the laser applicable in ablation process by
ultraviolet absorption, and capable of emitting ultraviolet rays at
specific wavelength .lamda.. It is further preferred to use the
laser capable of focusing the laser beam into a narrow width of 20
.mu.m or less and emitting ultraviolet rays of 355 nm.
More specifically, the laser having oscillation wavelength of 400
nm or less is preferred, such as KrF excimer laser of oscillation
wavelength 248 nm, XeCl excimer laser of 308 nm, and YAG laser
having third harmonic wave (355 nm), fourth harmonic wave (266 nm),
or wavelength of 400 nm or more, and in the case of such laser,
light absorption of ultraviolet region passing through multi-photon
absorption process is possible, and further examples include
titanium sapphire laser around wavelength of 750 to 800 nm capable
of cutting in a width of 20 .mu.m or less by multi-photon
absorption ablation, and laser with pulse width of 1e.sup.-9 sec
(0.000000001) or less.
The workpiece is not particularly specified as far as it can be
processed by ultraviolet absorption ablation of laser beam emitted
from the laser, and may include, among others, sheet material,
circuit board, semiconductor wafer, glass substrate, ceramic
substrate, metal substrate, semiconductor laser or other light
emitting or light detecting element board, MEMS (micro electro
mechanical system) board, semiconductor package, cloth, leather,
and paper.
The protective sheet and manufacturing method of the invention are
preferably applied particularly in processing of sheet material,
circuit board, semiconductor wafer, glass substrate, ceramic
substrate, metal substrate, semiconductor laser light emitting or
light detecting element board, MEMS board, and semiconductor
package.
Various sheet materials include, for example, macromolecular films
and nonwoven cloths made of polyimide resin, polyester resin, epoxy
resin, urethane resin, polystyrene resin, polyethylene resin,
polyamide resin, polycarbonate resin, silicone resin, fluorine
resin, etc., and further sheets made of such resins provided with
physical or optical functions by drawing, impregnation or other
processes, metal sheets of copper, aluminum, stainless steel, and
others, and the macromolecular film and/or metal sheet laminated
directly or by way of adhesive or the like.
Examples of the circuit board include one-side, double-side or
multi-layer flexible printed board, rigid board of glass epoxy,
ceramic or metal core substrate, and optical circuit or
opto-electrical mixed circuit board formed on glass or polymer.
Metal materials include both semimetals and alloys, for example,
gold, SUS, copper, iron, aluminum, stainless steel, silicon,
titanium, nickel, tungsten, and their processed materials
(semiconductor wafer, metal board, etc.).
In the tenth and twelfth aspects of the invention, the organic
workpiece is not particularly specified as far as it can be
processed by ultraviolet absorption ablation of laser beam emitted
from the laser, and may include, among others, sheet material,
cloth, leather, and paper.
Various sheet materials include, for example, macromolecular films
and nonwoven cloths, and sheets made of such resins provided with
physical or optical functions by drawing, impregnation or other
processes.
In the eleventh and thirteenth aspects of the invention, the
inorganic workpiece is not particularly specified as far as it can
be processed by ultraviolet absorption ablation of laser beam
emitted from the laser, and may include, among others, circuit
board, semiconductor wafer, glass substrate, ceramic substrate,
metal substrate, semiconductor laser or other light emitting or
light detecting element board, MEMS board, and semiconductor
package.
Metal materials include both semimetals and alloys, for example,
gold, SUS, copper, iron, aluminum, stainless, silicon, titanium,
nickel, tungsten, and their processed materials.
The protective sheet of the invention is a sheet used when
processing the workpiece by ultraviolet ablation of laser beam.
The protective sheet in the first aspect of the invention is
preferred to be less than 50% in the light transmissivity in the
laser beam (ultraviolet ray) absorption region. The protective
sheet may be formed of base material alone, or may have an adhesive
layer provided on the base material.
The protective sheet in the second aspect of the invention has at
least an adhesive layer provided on a base material, and the
etching rate of the base material is 0.4
[(.mu.m/pulse)/(J/cm.sup.2)] or more.
In the third aspect of the invention, a protective sheet having at
least an adhesive layer on a base material is used. It is necessary
to select and use a protective sheet of which extinction
coefficient ratio is 1 or more. On the other hand, in the case of
laser processing of metal material (fourth aspect of the
invention), it is necessary to select and use a protective sheet
having a base material of which extinction coefficient in
ultraviolet region wavelength .lamda. of 20 cm.sup.-1 or more.
In the manufacturing method of laser processed parts according to
the fifth aspect of the invention, a protective sheet having at
least an adhesive layer on a base material is used. It is necessary
to select and use a protective sheet of which density ratio is 1 or
more. On the other hand, in the case of laser processing of metal
material (sixth aspect of the invention), it is necessary to select
and use a protective sheet having a base material of which density
is 1.1 g/cm.sup.3 or more.
In the manufacturing method of laser processed parts according to
the seventh aspect of the invention, a protective sheet having at
least an adhesive layer on a base material is used. It is necessary
to select and use a protective sheet of which ratio of tensile
strength of protective sheet to tensile strength of workpiece
(tensile strength ratio=tensile strength of protective
sheet/tensile strength of workpiece) is 1 or more. On the other
hand, in the case of laser processing of metal material (eighth
aspect of the invention), it is necessary to select and use a
protective sheet having a base material of which tensile strength
is 100 MPa or more.
In the manufacturing method of laser processed parts according to
the ninth aspect of the invention, a protective sheet having at
least an adhesive layer on a base material is used. It is necessary
to select and use a protective sheet of which specific heat ratio
is less than 1.
In the manufacturing method of laser processed parts according to
the tenth aspect of the invention, a protective sheet having at
least an adhesive layer on a base material is used. It is necessary
to select and use a protective sheet of which refractive index
ratio is 1 or more in the case of laser processing of organic
workpiece. On the other hand, in the case of laser processing of
inorganic workpiece (eleventh aspect of the invention), it is
necessary to select and use a protective sheet having a base
material of which refractive index at wavelength 546 nm is 1.53 or
more.
In the manufacturing method of laser processed parts according to
the twelfth aspect of the invention, a protective sheet having at
least an adhesive layer on a base material is used. It is necessary
to select and use a protective sheet of which total coupling energy
ratio is less than 1 in the case of laser processing of organic
workpiece. On the other hand, in the case of laser processing of
inorganic workpiece (thirteenth aspect of the invention), it is
necessary to select and use a protective sheet having a base
material of which total coupling energy A is less than 800 kJ/mol.
Values of total coupling energies A and B are obtained from the
coupling energy values mentioned, for example, in the publication
(Cox, J. D. and Pilcher, G., Thermochemistry of organic and
organometallic compounds, Academic Press, New York, 1970).
Forming materials of base material include, for example,
polyethylene terephthalate, polyethylene naphthalate, polystyrene,
polycarbonate, polyimide, (meth)acrylic polymer, polyurethane,
silicone rubber, polyethylene, polypropylene, polyethylene oxide,
and other polyolefin polymers, and are not limited to these
examples alone. These materials may be used either alone or in
combination of two or more types. Above all, it is preferred to use
an aromatic polymer, and particularly it is preferred to use
polyimide, polyethylene naphthalate, or polycarbonate.
In the third and fourth aspects of the invention, it is preferred
to use a material of high extinction coefficient, such as
polyimide, polyethylene naphthalate, polystyrene, polycarbonate,
other aromatic polymers, and silicone rubber.
In the fifth and sixth aspects of the invention, it is preferred to
use a material of relatively high density, such as polyethylene
naphthalate, polyurethane, polyimide, and silicone rubber.
In the seventh and eighth aspects of the invention, in order to
enhance the tensile strength of base material, it is preferred to
use aromatic polymer and silicone rubber, and in particular it is
preferred to use polyimide, polyethylene naphthalate, polystyrene,
or polycarbonate.
In the ninth aspect of the invention, it is preferred to use a
material of relatively small specific heat, such as polyethylene
terephthalate, polyethylene naphthalate, polystyrene, polyurethane,
and polycarbonate.
In the tenth and eleventh aspects of the invention, it is preferred
to use a material of high refractive index at wavelength 546 nm,
such as polyimide, polyethylene naphthalate, polystyrene,
polycarbonate, other aromatic polymers, and silicone rubber.
In the twelfth and thirteen aspects of the invention, in order to
lower the value of total coupling energy A, it is preferred to use
aromatic polymer, and in particular it is preferred to use
polyimide, polyethylene terephthalate, polyethylene naphthalate,
polystyrene, or polycarbonate.
Preferably, a filler should be added to the base material. The
filler is a material added for keeping the light transmissivity in
laser beam absorption region at less than 50% (first aspect of the
invention), keeping the etching rate at 0.4 or more (second aspect
of the invention), heightening the extinction coefficient of base
material (third and fourth aspects of the invention), heightening
the tensile strength of base material (seventh and eighth aspects
of the invention), or heightening the refractive index of base
material (tenth and eleventh aspects of the invention), and its
examples include pigment, dyestuff, coloring matter, Au, Cu, Pt, Ag
and other fine metal particles, metal colloid, carbon and other
inorganic fine particles.
The coloring matter is not particularly specified as far as it can
absorb the light of specific wavelength of the user being used
(light of ultraviolet region wavelength .lamda.), and the dyestuff
includes various types such as basic dye, acid dye, and direct dye.
Examples of dyestuff and coloring matter include nitro dye, nitroso
dye, stilbene dye, pyrazolone dye, thiazole dye, azo dye, polyazo
dye, carbonium dye, quinoanyl dye, indophenol dye, indoaniline dye,
indamine dye, quinonimine dye, azine dye, oxidizing dye, oxazine
dye, thiazine dye, acryzine dye, diphenyl methane dye, triphenyl
methane dye, xanthene dye, thioxanthene dye, sulfurizing dye,
pyridine dye, pyridone dye, thiadiazole dye, thiophene dye, benzoin
thiazole dye, quinoline dye, indigo dye, thioindigo dye,
anthraquinone dye, benzophenone dye, benzoquinone dye,
naphthoquinone dye, phthalocyanine dye, cyanine dye, methine dye,
polymethine dye, azomethine dye, condensed methine dye, naphthal
imide dye, perinone dye, triaryl methane dye, xanthene dye,
aminoketone dye, oxyketone dye, and indigoid dye. These dyes may be
used either alone or in combination of two or more types.
The dyestuff or coloring matter may be nonlinear optical coloring
matter. The nonlinear optical coloring matter is not particularly
specified, and known nonlinear optical coloring matters may be used
(for example, benzene nonlinear optical coloring matter, stilbene
nonlinear optical coloring matter, cyanine nonlinear optical
coloring matter, azo nonlinear optical coloring matter, rhodamine
nonlinear optical coloring matter, biphenyl nonlinear optical
coloring matter, chalcone nonlinear optical coloring matter, and
cyanocinnamic acid nonlinear optical coloring matter).
Further, as the dyestuff or coloring matter, so-called "functional
coloring matter" may be also used. The functional coloring matter
is composed of carrier forming material and carrier moving
material. The carrier forming material is, for example, perylene
pigment, quinone pigment, squalilium coloring matter, azulenium
coloring matter, thiapyrilium coloring matter, and bisazo pigment.
The carrier moving material includes oxadiazole derivative, oxazole
derivative, pyrazoline derivative, hydrozine derivative, aryl amine
derivative, etc.
The content of the filler may be properly adjusted depending on the
light transmissivity of the base polymer used (first aspect of the
invention), the etching rate of the base polymer (second aspect of
the invention), the extinction coefficient of base polymer and
extinction coefficient of workpiece (third and fourth aspects of
the invention), the relation of tensile strength of base polymer
and tensile strength of workpiece (seventh and eighth aspects of
the invention), or the refractive index of base polymer or
refractive index of workpiece (tenth and eleventh aspects of the
invention), but usually it is preferred to be about 2 to 20 parts
by weight in 100 parts by weight of base polymer, and more
preferably about 2 to 10 parts by weight.
The base material may be made of a single layer or plural layers.
It may be formed as membrane, mesh or other shape.
The thickness of base material may be properly adjusted within a
range not spoiling the handling and working efficiency at each step
of adhering to the workpiece, cutting or drilling of workpiece, and
peeling and collecting of cut pieces, but usually it is about 500
.mu.m or less, or preferably about 3 to 300 .mu.m, or more
preferably 5 to 250 .mu.m. The surface of base material is treated
by ordinary surface treatment for enhancing the contact with the
adjacent material or retaining property, such as chromate
treatment, ozone exposure, flame exposure, high voltage electric
impact exposure, ionization radiation treatment, and other chemical
or physical treatment.
Forming materials of adhesive layer include known adhesive
materials including (meth)acrylic polymer and rubber polymer.
Monomer components for forming (meth)acrylic polymer are alkyl
(meth)acrylates having alkyl radical of straight chain or branch
chain with 30 carbon atoms or less, or preferably 4 to 18 carbon
atoms, including, for example, methyl radical, ethyl radical,
n-propyl radical, isopropyl radical, n-butyl radical, t-butyl
radical, isobutyl radical, amyl radical, isoamyl radical, hexyl
radical, heptyl radical, cyclohexyl radical, 2-ethyl hexyl radical,
octyl radical, iso-octyl radical, nonyl radical, isononyl radical,
decynol radical, isodecyl radical, undecyl radical, lauryl radical,
tridecyl radical, tetradecyl radical, stearyl radical, octadecyl
radical, and dodecyl radical. These alkyl (meth)acrylates may be
used either alone or in combination of two or more types.
In order to modify the adhesiveness, coagulation or heat resistance
of (meth)acrylic polymer, other monomer components than mentioned
above may be copolymerized as required.
Other monomers capable of forming such polymers include, for
example, acrylic acid and methacrylic acid,
carboxyethyl(meth)acrylate and carboxypentyl(meth)acrylate,
itaconic acid and maleic acid, fumaric acid and crotonic acid or
other monomer containing carboxyl radical, maleic anhydride and
itaconic anhydride or other monomer of acid anhydride,
(meth)acrylic acid 2-hydroxyl ethyl and (meth)acrylic acid
2-hydroxyl propyl, (meth)acrylic acid 4-hydroxyl butyl and
(meth)acrylic acid 6-hydroxylhexyl, (meth)acrylic acid
8-hydroxyoctyl and (meth)acrylic acid 10-hydroxyl decyl,
(meth)acrylic acid 12-hydroxylauryl and (4-hydroxymethyl
cyclohexyl)-methylacrylate or other monomer containing hydroxyl
radical, styrene sulfonic acid and acrylic sulfonic acid,
2-(meth)acrylic amide-2-methyl propane sulfonic acid and
(meth)acrylic amide propane sulfonic acid, sulfopropyl
(meth)acrylate and (meth)acryloyl oxynaphthalene sulfonic acid or
other monomer containing sulfonic acid radical, 2-hydroxy ethyl
acryloyl phosphate or other monomer containing phosphoric acid
radical, (meth)acrylic amide, (meth)acrylic acid N-hydroxymethyl
amide, (meth)acrylic acid alkyl aminoalkyl ester (for example,
dimethyl aminoethyl methacrylate), t-butyl aminoethyl methacrylate,
etc.), N-vinyl pyrrolidone, acryloyl morphorine, vinyl acetate,
styrene, acrylonitrile, etc.
In addition, for the purpose of crosslinking of acrylic polymer or
the like, multifunctional monomers and the like may be added as
required as monomer component for copolymerization. Examples of
such monomer include hexane diol di(meth)acrylate and
(poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol
di(meth)acrylate and neopentyl glycol di(meth)acrylate,
pentaerythritol di(meth)acrylate and trimethylol propane
tri(meth)acrylate, pentaerythritol hexatri(meth)acrylate and
dipentaerythritol hexa(meth)acrylate, epoxy acrylate and polyester
acrylate, urethane acrylate, and others. One type or two or more
types of multifunctional monomer may be used.
The content of multifunctional monomer is preferred to be 30 wt %
or less of the total monomer content from the viewpoint of
adhesiveness and others, and more preferably 20 wt % or less.
To prepare (meth)acrylic polymer, various methods may be applied,
for example, solution polymerization method of mixture containing
one, two or more types of monomer components, emulsification
polymerization method, block polymerization, and suspension
polymerization method.
Polymerization initiator includes peroxides such as hydrogen
peroxide, benzoyl peroxide, and t-butyl peroxide. It is preferred
to use alone, but it may be combined with reducer to be used as
redox polymerization initiator. The reducer includes sulfite,
hydrogen sulfite, iron, copper, cobalt salt, or other ionized salt,
triethanolamine and other amines, aldose, ketose, and other
reducing sugar. An azo compound is also a preferred polymerization
initiator, and its example includes 2,2'-azobis-2-methylpropio
amidinate, 2,2'-azobis-2,4-dimethyl valeronitrile,
2,2'-azobis-N,N'-dimethylene isobutyl amidinate, 2,2'-azobis
isobutyronitrile, and 2,2'-azobis-2-methyl-N-(2-hydroxy ethyl)
propione amide. Two or more types of these polymerization
initiators may be used in combination.
Reaction temperature is usually about 50 to 85.degree. C., and the
reaction time is about 1 to 8 hours. Among the manufacturing
method, solution polymerization is preferred, and as solvent of
(meth)acrylic polymer, generally, ethyl acetate, toluene, and other
polar solvents are used. The solution concentration is generally
about 20 to 80 wt %.
The adhesive agent may be properly combined with a crosslinking
agent for raising the number-average molecular weight of
(meth)acrylic polymer used as base polymer. Examples of
crosslinking agent include polyisocyanate compound, epoxy compound,
aziridine compound, melamione resin, urea resin, anhydrous
compound, polyamine, and polymer containing carboxyl radical. When
the crosslinking agent is used, its content must be determined so
that the peel adhesive strength may not be lowered too much, and
generally it is preferred to add by about 0.01 to 5 parts by weight
in 100 parts by weight of base polymer. The adhesive agent for
forming the adhesive layer may be also combined with other known
additives as required, in addition to the specified components,
such as adhesion improver, aging retardant, filler, coloring
matter, and others.
To improve peeling from workpiece, the adhesive agent is preferred
to be radiation curing type adhesive which is cured by radiation
such as ultraviolet ray or electron ray. When a radiation curing
type adhesive is used as the adhesive agent, since the adhesive
layer is irradiated with radiation after laser processing, the base
material is preferred to have a sufficient radiation
transmissivity.
The radiation curing type adhesive includes, for example, radiation
curing type adhesive prepared by blending radiation curing monomer
component or oligomer component to the (meth)acrylic polymer.
Examples of monomer component or oligomer component of radiation
curing type to be blended include urethane; (meth)acrylate
oligomer, trimethylol propane tri(meth)acrylate, tetramethylol
methane tetra(meth)acrylate, tetraethylene glycol di(meth)acrylate,
pentaerythritol tri(meth)acrylate, pentaerythritol
tetra(meth)acrylate, dipentaerythritol monohydroxy
penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,
1,4-butylene glycol di(meth)acrylate, 1,6-hexane diol
(meth)acrylate, and other ester compounds of (meth)acrylate and
polyhydric alcohol; 2-propenyl-3-butenyl cyanurate,
tris(2-methacryloxy ethyl) isocyanurate, and other isocyanurate or
isocyanurate compounds. One type or two or more types of monomer
component or oligomer component may be used.
The blending amount of radiation curing monomer component or
oligomer component is not particularly specified, but considering
the adhesiveness, it is preferred to add by about 5 to 500 parts by
weight in 100 parts by weight of base polymer such as (meth)acrylic
polymer for composing the adhesive agent, and more preferably by
about 70 to 150 parts by weight.
As the radiation curing type adhesive, further, a base polymer
having carbon-carbon double bond in the polymer side chain, main
chain or main chain end may be used. Such base polymer is preferred
to have (meth)acrylic polymer as basic skeleton. In this case,
radiation curing type monomer component or oligomer component may
not be added, and its use is free.
The radiation curing type adhesive should contain a
photopolymerization initiator when curing by ultraviolet ray or the
like.
Examples of photopolymerization initiator include 4-(2-hydroxy
ethoxy) phenyl (2-hydroxy-2-propyl) ketone, alpha-hydroxy-alpha,
alpha-methyl acetophenone, methoxy acetophenone,
2,2-dimethoxy-2-saphenyl acetophenone, 2,2-diethoxy acetophenone,
1-hydroxy siurohexyl phenyl ketone,
2-methyl-1-(4-(methylthio)-phenylco-2-morpholinopropane-1, other
acetophenone compounds, benzoin ethyl ether, benzoin
isopropylether, anizoin methyl ether, other benzoin ether
compounds, 2-methyl-2-hydroxypropiophenone, other alpha-ketol
compounds, benzyl dimethyl ketal, other ketal compounds,
2-naphthalene sulfonyl chloride, other aromatic sulfonyl chloride
compounds, 1-phenone-1,1-propane dione-2-(O-ethoxy carbonyl) oxime,
other photoactive oxime compounds, benzophenone and benzoyl benzoic
acid, 3,3'-dimethyl-4-methoxybenzophenone, other benzophenone
compounds, thioxanthone, 2-chlorothioxanthone, 2-methl
thioxanthone, 2,4-dimethyl thioxanthone, isopropyl thioxanthone,
2,4-dichlorothoixanthone, 2,4-diethyl thioxanthone, 2,4-diisopropyl
thioxanthone, other thioxanthone compounds, and also campher
quinone, ketone halide, acyl phosphino oxide, acyl phosphoanate,
etc.
The content of photopolymerization initiator is preferred to be
about 0.1 to 10 parts by weight in 100 parts by weight of base
polymer such as (meth)acrylic polymer for composing the adhesive
agent, or more preferably about 0.5 to 5 parts by weight.
The protective sheet can be manufactured by applying an adhesive
solution on the surface of a base material, and drying (or heating
and crosslinking as required) to form an adhesive layer.
Alternatively, an adhesive layer may be separately formed on a
peeling liner, and it may be adhered to the base material. The
adhesive layer may one layer or two or more layers. As required, a
separator may be formed on the surface of the adhesive layer.
The adhesive layer is preferred to be low in content of low
molecular substance from the viewpoint of prevention of
contamination on workpiece. From such point of view, the
number-average molecular weight of (meth)acrylic polymer is
preferred to be 300,000 or more, more preferably 400,000 to
3,000,000, and further preferably 800,000 to 3,000,000.
The thickness of adhesive layer may be properly selected within a
range not peeling from the workpiece, and is preferred to be about
5 to 300 .mu.m, more preferably about 10 to 100 .mu.m, and further
preferably about 10 to 50 .mu.m.
The adhesive strength of adhesive layer is preferred to be 20 N/20
mm or less on the basis of adhesive strength (90-degree peel value,
peeling speed 300 mm/min) at ordinary temperature (before laser
emission) on SUS304, and more preferably 0.001 to 10 N/20 mm, or
further preferably 0.01 to 8 N/20 mm.
The separator is used as required for protecting label processing
or adhesive layer. The material for the separator includes paper,
polyethylene, polypropylene, polyethylene terephthalate, and other
synthetic resin film. The surface of the separator may be properly
treated for improving the peeling performance from the adhesive
layer by, for example, silicone treatment, long-chain alkyl
treatment, fluorine treatment or other peeling treatment. As
required, further, ultraviolet transmission preventive treatment
may be applied to prevent the protective sheet from reacting by
environmental ultraviolet rays. The thickness of the separator is
usually 10 to 200 .mu.m, preferably about 25 to 100 .mu.m.
The following is the explanation of manufacturing method of laser
processed parts by ultraviolet absorption ablation of laser beam
using the protective sheet of the invention. For example, in the
case of cutting process, as shown in FIG. 1 and FIG. 3, a
protective sheet 2, a workpiece (or metal workpiece) 1, and an
adhesive sheet 3 are glued together by known means such as roll
laminator and press to obtain a laminated body 4 of protective
sheet, workpiece and adhesive sheet, which is disposed on an
adsorption plate 6 of an adsorption stage 5, and a laser beam 7 is
emitted to the laminated body 4 from a specified laser oscillator
by focusing and emitting on the protective sheet 2 by means of a
lens, and the laser emission position is moved along the specified
processing line to cut the workpiece. The adhesive sheet 3 disposed
at the exit side of laser beam of the workpiece plays the role of
supporting and fixing the workpiece before laser processing, and
plays the role of preventing the cut piece from falling after laser
processing, and a sheet of low laser processability is used. As the
adhesive sheet 3, a general material having an adhesive layer
laminated on a base material may be used without particular
limitation.
Laser beam moving means includes galvano scan, X-Y stage scan, mask
image processing, and other known laser processing method.
The laser processing condition is not particularly specified as far
as the protective sheet 2 and workpiece 1 can be cut off
completely, but in order to prevent cutting of adhesive sheet 3, it
is preferred to control within 2 times of energy condition for
cutting the workpiece 1.
The cutting allowance (section groove) can be narrowed by reducing
the beam diameter of focusing unit of laser beam, but in order to
enhance the section end precision, it is preferred to satisfy the
condition of beam diameter (.mu.m)>2.times.(laser beam moving
speed (.mu.m/sec)/laser beam repetition frequency (Hz)).
In the case of drilling, as shown in FIG. 2, a protective sheet 2,
a workpiece 1, and an adhesive sheet 3 are glued together by known
means such as roll laminator and press to obtain a laminated body 4
of protective sheet, workpiece and adhesive sheet, which is
disposed on an adsorption plate 6 of an adsorption stage 5, and a
laser beam 7 is emitted to the laminated body 4 from a specified
laser oscillator by focusing and emitting on the protective sheet 2
by means of a lens, and a hole is formed.
The hole is formed by known laser processing method such as
punching by galvano scan, X-Y stage scan, mask imaging. The laser
processing condition may be determined at the optimum value on the
basis of the ablation threshold of workpiece. To prevent drilling
of adhesive sheet 3, it is preferred to control within 2 times of
energy condition for drilling the workpiece 1.
Decomposition products can be scattered and removed efficiently by
blowing gas of helium, nitrogen or oxygen to the laser processing
unit.
In cutting process of semiconductor wafer, as shown in FIG. 4, one
side of a semiconductor wafer 8 is adhered to an adhesive sheet 3
disposed on an adsorption stage 5, a protective sheet 2 is disposed
at other side, and a laser beam 7 generated from a specified laser
oscillator is focused and emitted to the protective sheet 2 by a
lens, and the laser emission position is moved along the specified
processing line, so that it is cut off. Laser beam moving means
includes galvano scan, X-Y stage scan, mask image processing, and
other known laser processing method. The laser processing condition
is not particularly specified as far as the protective sheet 2 and
semiconductor wafer 8 can be cut off completely, while the adhesive
sheet 3 is not cut off.
In such cutting process of semiconductor wafer, after cutting into
individual semiconductor chips, the individual semiconductor chips
can be picked up and collected by known methods such as the method
of picking up by using a poking pin called needle by a conventional
die bonder or other device, or a method disclosed in Japanese
Laid-open Patent No. 2001-118862.
In the manufacturing method of laser processed parts of the
invention, after laser processing, the protective sheet 2 is peeled
off from the laser processed part 10. The peeling method is not
particularly specified, but it is important not to apply stress to
cause permanent set of laser processed part 10 at the time of
peeling. For example, when radiation curing type adhesive is used
in the adhesive layer, the adhesiveness is lowered by curing the
adhesive layer by radiation irradiation depending on the type of
adhesive agent. By irradiation with radiation, the adhesiveness of
the adhesive layer is lowered by curing, and it is easier to peel
off. Irradiation means of radiation is not particularly specified,
and, for example, ultraviolet radiation may be used.
In the manufacturing method of laser processed parts of the first
aspect of the invention, by using the protective sheet,
decomposition products generated from the laser beam exposed part
stick to the surface of the protective sheet which covers the
workpiece, sticking of decomposition products to the surface of the
workpiece can be effectively prevented. Besides, when using the
protective sheet large in the laser energy utilization efficiency
of less than 50% of light transmissivity in the laser beam
absorption region, the protective sheet is eroded by the laser beam
earlier than the workpiece, and after the laser beam exposed part
of the protective sheet is eroded, the workpiece in the lower layer
is eroded. Accordingly, the decomposition products of the workpiece
scatter outside from the eroded portion of the protective sheet,
and contamination at the interface of the protective sheet and
workpiece can be suppressed.
In the manufacturing method of laser processed parts of the second
aspect of the invention, by using the protective sheet of which
etching rate of base material is 0.4 or more, the protective sheet
is likely to be etched by the laser beam earlier than the
workpiece, and after the laser beam exposed part of the protective
sheet is sufficiently etched, the workpiece in the lower layer is
etched. Accordingly, the decomposition products of the workpiece
scatter outside efficiently from the etching portion of the
protective sheet, and contamination at the interface of the
protective sheet and workpiece can be suppressed.
In the manufacturing method of laser processed parts of the third
(or fourth) aspect of the invention, by using the protective sheet
of which extinction coefficient ratio is 1 or more (or protective
sheet having a base material of which extinction coefficient at
ultraviolet region wavelength .lamda. is 20 cm.sup.-1 or more), the
protective sheet is more likely to be etched than the workpiece (or
metal material), and after the laser beam exposed part of the
protective sheet is sufficiently etched, the workpiece in the lower
layer is etched. Accordingly, the decomposition products of the
workpiece scatter outside efficiently from the etching portion of
the protective sheet, and contamination at the interface of the
protective sheet and workpiece can be suppressed.
In the manufacturing method of laser processed parts of the fifth
aspect of the invention, by using the protective sheet of which
density ratio is 1 or more, the protective sheet is more likely to
be etched than the workpiece, and after the laser beam exposed part
of the protective sheet is sufficiently etched, the workpiece in
the lower layer is etched. In the manufacturing method of laser
processed parts of the sixth aspect of the invention, by using the
protective sheet having a base material of which density is 1.1
g/cm.sup.3 or more, the protective sheet is more likely to be
etched than the metal material, and after the laser beam exposed
part of the protective sheet is sufficiently etched, the metal
material in the lower layer is etched. Accordingly, the
decomposition products of the workpiece (metal material) scatter
outside efficiently from the etching portion of the protective
sheet, and contamination at the interface of the protective sheet
and workpiece (metal material) can be suppressed.
In the manufacturing method of laser processed parts of the seventh
(or eighth) aspect of the invention, by using the protective sheet
of which tensile strength ratio is 1 or more (or protective sheet
of which tensile strength is 100 MPa or more), the protective sheet
is more likely to be etched than the workpiece (or metal material),
and after the laser beam exposed part of the protective sheet is
sufficiently etched, the workpiece in the lower layer is etched.
Accordingly, the decomposition products of the workpiece scatter
outside efficiently from the etching portion of the protective
sheet, and contamination at the interface of the protective sheet
and workpiece can be suppressed.
In the manufacturing method of laser processed parts of the ninth
aspect of the invention, by using the protective sheet of which
density specific heat ratio is less than 1, the protective sheet is
more likely to be etched than the workpiece, and after the laser
beam exposed part of the protective sheet is sufficiently etched,
the workpiece in the lower layer is etched. Accordingly, the
decomposition products of the workpiece scatter outside efficiently
from the etching portion of the protective sheet, and contamination
at the interface of the protective sheet and workpiece can be
suppressed.
In the manufacturing method of laser processed parts of the tenth
(or eleventh) aspect of the invention, by using the protective
sheet of which refractive index ratio is 1 or more (or protective
sheet having a base material of which refractive index at
wavelength 546 nm is 1.53 or more), the protective sheet is more
likely to be etched than the workpiece, and after the laser beam
exposed part of the protective sheet is sufficiently etched, the
workpiece in the lower layer is etched. Accordingly, the
decomposition products of the workpiece scatter outside efficiently
from the etching portion of the protective sheet, and contamination
at the interface of the protective sheet and workpiece can be
suppressed.
In the manufacturing method of laser processed parts of the twelfth
(or thirteenth) aspect of the invention, by using the protective
sheet of which total coupling energy ratio is less than 1 (or
protective sheet having a base material of which total coupling
energy A is less than 800 kJ/mol), the protective sheet is more
likely to be etched than the workpiece, and after the laser beam
exposed part of the protective sheet is sufficiently etched, the
workpiece in the lower layer is etched. Accordingly, the
decomposition products of the workpiece scatter outside efficiently
from the etching portion of the protective sheet, and contamination
at the interface of the protective sheet and workpiece can be
suppressed.
Therefore, according to the manufacturing methods of the invention,
decomposition products do not stick to the interface of the
protective sheet and workpiece (laser processed part), and after
laser processing of workpiece, the protective sheet can be easily
peeled off from the laser processed parts, and the laser processing
precision of workpiece can be also enhanced.
EXAMPLES
Exemplary embodiments of the invention are described specifically
below, but it must be noted that the invention is not limited by
these embodiments alone.
(First Aspect of the Invention)
[Measurement of Number-Average Molecular Weight]
Number-average molecular weight of synthesized (meth)acrylic
polymer was measured in the following method. By dissolving the
synthesized (meth)acrylic polymer in THF at 0.1 wt %, the
number-average molecular weight was calculated by polystyrene
conversion by using GPC (gel permeation chromatography). The
measuring condition is as follows.
GPC apparatus: HLC-8210GPC of Tosoh corporation
Column: (GMHHR-H)+(GMHHR-H)+(G2000HHR) of Tosoh corporation
Flow rate: 0.8 ml/min
Concentration: 0.1 wt %
Injection: 100 .mu.l
Column temperature: 40.degree. C.
Eluate: THF
[Measurement of Light Transmissivity]
Cutting base material and protective sheet into proper size, the
light transmissivity was measured at wavelength 355 nm by using
measuring apparatus U-3400 (Hitachi, Ltd.). The protective sheet
was measured from the adhesive layer side.
Example 1
On a base material (thickness: 20 .mu.m, light transmissivity at
wavelength 355 nm: 0%) made of polyethylene naphthalate (weight
ratio of aromatic ring in repetition unit: 64 wt %), ultraviolet
curable acrylic adhesive solution (1) was applied, and dried to
form an adhesive layer (thickness 10 .mu.m), and a protective sheet
was obtained. The light transmissivity of this protective sheet at
wavelength 355 nm was 0%.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 800,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 60/40/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, and 5
parts by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator were added together with 650 parts by
weight of toluene, and the mixture was uniformly dissolved and
stirred, and the acrylic adhesive solution (1) was prepared.
On one side of silicon wafer of 100 .mu.m in thickness, the
manufactured protective sheet was adhered by a roll laminator, and
a silicon wafer with protective sheet was fabricated. On an XY
stage mounting an adsorption plate of glass epoxy resin, the
silicon wafer with protective sheet was placed with the protective
sheet upside. Using YAG laser of wavelength 355 nm, average output
5 W and repetition frequency 30 kHz, third harmonic wave (355 nm)
was focused on the surface of silicon wafer with protective sheet
in a diameter of 25 .mu.m by f.theta. lens, and the surface was
scanned by laser beam at a speed of 20 mm/sec by galvano scanner,
and was cut off. At this time, cutting of protective sheet and
silicon wafer was confirmed. After peeling off the protective
sheet, the protective sheet gluing surface of the silicon wafer
(the laser beam incident side) was observed particularly in the
laser processing area, and decomposition products (deposits) were
not observed.
Comparative Example 1
The silicon wafer was processed by laser in the same manner as in
Example 1, except that protective sheet was not glued to one side
of the silicon wafer. When the surface of the laser beam incident
side of the silicon wafer was observed, sticking of much residue of
scattering decomposition products was recognized.
Reference Example 1
The silicon wafer was processed by laser in the same manner as in
Example 1, except that polyvinyl alcohol sheet (thickness: 50
.mu.m, light transmissivity at wavelength 355 nm: 84.4%) was used
as base material of protective sheet. As a result, the protective
sheet was not cut off sufficiently, and the silicon wafer in the
lower layer was processed by laser, and foams including
decomposition product residue were generated between the protective
sheet and silicon wafer. By peeling off the protective sheet, the
opening area of the laser beam incident side of the silicon wafer
was observed, and sticking of residue of scattering decomposition
products of silicon wafer was recognized.
Example 2
On a base material (thickness: 13 .mu.m, light transmissivity at
wavelength 355 nm: 0%) made of polyimide (weight ratio of aromatic
ring in repetition unit: 64 wt %), ultraviolet curable acrylic
adhesive solution (2) was applied, and dried to form an adhesive
layer (thickness 10 .mu.m), and a protective sheet was obtained.
The light transmissivity of this protective sheet at wavelength 355
nm was 0%.
The acrylic adhesive solution (2) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 500,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, and 2-hydroxy ethyl acrylate at ratio by weight of
50/50/16, 20 parts by weight of 2-methacryloyl oxyethyl isocyanate
was added to react, and a carbon-carbon double bond was introduced
into the side chain in the polymer molecule (at this time, the side
chain is 13 atoms long). In 100 parts by weight of this polymer, 1
part by weight of polyisocyanate crosslinking agent (Coronate L)
and 3 parts by weight of alpha-hydroxy ketone (Irgacure 184) as
photopolymerization initiator were added together with 350 parts by
weight of toluene, and the mixture was uniformly dissolved and
stirred, and the acrylic adhesive solution (2) was prepared.
On a two-layer substrate forming a copper layer of 18 .mu.m in
thickness on a polyimide film of 25 .mu.m in thickness, a circuit
was formed by exposing, developing, and etching process, and a
flexible printed board was manufactured. The manufactured flexible
printed board and protective film were glued together by a roll
laminator, and a flexible printed board with protective sheet was
manufactured.
On an XY stage mounting a ceramic adsorption plate of alumina, the
flexible printed board with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of flexible printed board
with protective sheet in a diameter of 25 .mu.m by f.theta. lens,
and the surface was scanned by laser beam at a speed of 20 mm/sec
by galvano scanner, and was cut off. At this time, cutting of
protective sheet and flexible printed board was confirmed. After
peeling off the protective sheet, the protective sheet gluing
surface of the flexible printed board (the laser beam incident
side) was observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Example 3
The flexible printed board was processed by laser in the same
manner as in Example 2, except that polyethylene terephthalate film
(ratio by weight of aromatic ring in repetition unit: 41 wt %,
thickness: 50 .mu.m, light transmissivity at wavelength 355 nm:
44.9%) was used as base material of protective sheet. As a result,
cutting of protective sheet and flexible printed board was
confirmed. After peeling off the protective sheet, the protective
sheet gluing surface of the flexible printed board (the laser beam
incident side) was observed particularly in the laser processing
area, and decomposition products (deposits) were not observed.
Example 4
The flexible printed board was processed by laser in the same
manner as in Example 2, except that polycarbonate film (ratio by
weight of aromatic ring in repetition unit: 61 wt %, thickness: 20
.mu.m, light transmissivity at wavelength 355 nm: 0%) was used as
base material of protective sheet. As a result, cutting of
protective sheet and flexible printed board was confirmed. After
peeling off the protective sheet, the protective sheet gluing
surface of the flexible printed board (the laser beam incident
side) was observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Example 5
A base material for protective sheet was manufactured by forming a
sheet by casting a polymer obtained by copolymerization of
4-methyl-1-pentyne and 1,4-bis{2-[4-N,N-di(p-tolyl) amino)
phenyl]vinyl} benzine at ratio by weight of 97/3.
The flexible printed board was processed by laser in the same
manner as in Example 2, except that the above manufactured base
material (ratio by weight of aromatic ring in repetition unit: 2.4
wt %, thickness: 10 .mu.m, light transmissivity at wavelength 355
nm: 5%) was used as base material of protective sheet. As a result,
cutting of protective sheet and flexible printed board was
confirmed. After peeling off the protective sheet, the protective
sheet gluing surface of the flexible printed board (the laser beam
incident side) was observed particularly in the laser processing
area, and decomposition products (deposits) were not observed.
(Second Aspect of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
[Measurement of Etching Rate]
Using YAG laser shaped into tophat beam (maximum output 5 W,
repetition frequency 30 kHz), third harmonic wave (355 .mu.m) was
focused by f.theta. lens, and emitted to the base material surface
in the condition of pulse number 50 (pulses). After exposure, the
depth (.mu.m) of groove formed in the base material was measured by
optical microscope. The etching speed is calculated in the
following formula. Etching speed=groove depth(.mu.m)/pulse
number(pulses).
The energy fluence of YAG laser was 5 (J/cm.sup.2). The etching
rate is calculated in the following formula form the etching speed
and energy fluence. Etching rate=etching speed (.mu.m/pulse)/energy
fluence (J/cm.sup.2).
Example 1
On a base material made of polystyrene (thickness: 20 .mu.m,
etching rate: 0.48), ultraviolet curable acrylic adhesive solution
(1) was applied, and dried to form an adhesive layer (thickness 10
.mu.m), and a protective sheet was obtained.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 800,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 60/40/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, and 5
parts by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator were added together with 650 parts by
weight of toluene, and the mixture was uniformly dissolved and
stirred, and the acrylic adhesive solution (1) was prepared.
On one side of silicon wafer of 100 .mu.m in thickness, the
manufactured protective sheet was adhered by a roll laminator, and
a silicon wafer with protective sheet was fabricated. On an XY
stage mounting an adsorption plate of glass epoxy resin, the
silicon wafer with protective sheet was placed with the protective
sheet upside. Using YAG laser of wavelength 355 nm, average output
5 W and repetition frequency 30 kHz, third harmonic wave (355 nm)
was focused on the surface of silicon wafer with protective sheet
in a diameter of 25 .mu.m by f.theta. lens, and the surface was
scanned by laser beam at a speed of 20 mm/sec by galvano scanner,
and was cut off. At this time, cutting of protective sheet and
silicon wafer was confirmed. After peeling off the protective
sheet, the protective sheet gluing surface of the silicon wafer
(the laser beam incident side) was observed particularly in the
laser processing area, and decomposition products (deposits) were
not observed.
Comparative Example 1
The silicon wafer was processed by laser in the same manner as in
Example 1, except that protective sheet was not glued to one side
of the silicon wafer. When the processing area of the laser beam
incident side of the silicon wafer was observed, sticking of much
residue of scattering decomposition products was recognized.
Comparative Example 2
The silicon wafer was processed by laser in the same manner as in
Example 1, except that polyethylene sheet (thickness: 50 .mu.m,
etching rate: 0) was used as base material of protective sheet. As
a result, the protective sheet was not cut off, and the silicon
wafer in the lower layer was processed by laser, and foams
including decomposition product residue were generated between the
protective sheet and silicon wafer. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
silicon wafer was observed, and sticking of much residue of
decomposition products of silicon wafer was recognized.
Comparative Example 3
The silicon wafer was processed by laser in the same manner as in
Example 1, except that polyurethane sheet (thickness: 50 .mu.m,
etching rate: 0.26) was used as base material of protective sheet.
As a result, the protective sheet was not cut off, and the silicon
wafer in the lower layer was processed by laser, and foams
including decomposition product residue were generated between the
protective sheet and silicon wafer. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
silicon wafer was observed, and sticking of much residue of
decomposition products of silicon wafer was recognized.
Example 2
On a base material of silicone rubber (thickness: 20 .mu.m, etching
rate: 0.52), ultraviolet curable acrylic adhesive solution (2) was
applied, and dried to form an adhesive layer (thickness 10 .mu.m),
and a protective sheet was obtained.
The acrylic adhesive solution (2) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 500,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, and 2-hydroxy ethyl acrylate at ratio by weight of
50/50/16, 20 parts by weight of 2-methacryloyl oxyethyl isocyanate
was added to react, and a carbon-carbon double bond was introduced
into the side chain in the polymer molecule (at this time, the side
chain is 13 atoms long). In 100 parts by weight of this polymer, 1
part by weight of polyisocyanate crosslinking agent (Coronate L)
and 3 parts by weight of alpha-hydroxy ketone (Irgacure 184) as
photopolymerization initiator were added together with 400 parts by
weight of toluene, and the mixture was uniformly dissolved and
stirred, and the acrylic adhesive solution (2) was prepared.
On a two-layer substrate forming a copper layer of 18 .mu.m in
thickness on a polyimide film of 25 .mu.m in thickness, a circuit
was formed by exposing, developing, and etching process, and a
flexible printed board was manufactured. The manufactured flexible
printed board and protective film were glued together by a roll
laminator, and a flexible printed board with protective sheet was
manufactured.
On an XY stage mounting a ceramic adsorption plate of alumina, the
flexible printed board with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of flexible printed board
with protective sheet in a diameter of 25 .mu.m by f.theta. lens,
and the surface was scanned by laser beam at a speed of 20 mm/sec
by galvano scanner, and was cut off. At this time, cutting of
protective sheet and flexible printed board was confirmed. After
peeling off the protective sheet, the protective sheet gluing
surface of the flexible printed board (the laser beam incident
side) was observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Example 3
The flexible printed board was processed by laser in the same
manner as in Example 2, except that polyimide film (thickness: 13
.mu.m, etching rate: 0.95) was used as base material of protective
sheet. As a result, cutting of protective sheet and flexible
printed board was confirmed. After peeling off the protective
sheet, the protective sheet gluing surface of the flexible printed
board (the laser beam incident side) was observed particularly in
the laser processing area, and decomposition products (deposits)
were not observed.
Example 4
A polypropylene sheet of 20 .mu.m in thickness was manufactured by
mixing 99 parts by weight of polypropylene and 1 part by weight of
carbon black, and fusing and extruding.
The silicon wafer was processed by laser in the same manner as in
Example 2, except that the above manufactured polypropylene
(etching rate: 0.45) was used as base material of protective sheet.
After peeling off the protective sheet, the protective sheet gluing
surface of the flexible printed board (the laser beam incident
side) was observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
As clear from the examples and comparisons, by using the protective
sheet having a base material of which etching rate is 0.4 or more,
contamination of surface of workpiece by decomposition products can
be effectively suppressed.
(Third and Fourth Aspects of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
[Measurement of Extinction Coefficient]
The extinction coefficient of the base material and workpiece was
determined by measuring the absorbance at wavelength 355 nm by
using a spectrophotometer (U-3410 of Hitachi, Ltd.), and
calculating from the value of absorbance.
Example 1
The workpiece was a polystyrene sheet (thickness: 100 .mu.m,
extinction coefficient; 48 cm.sup.-1). On a base material made of
polyurethane (thickness: 20 .mu.m, extinction coefficient: 125
cm.sup.-1), ultraviolet curable acrylic adhesive solution (1) was
applied, and dried to form an adhesive layer (thickness 10 .mu.m),
and a protective sheet was obtained. The extinction coefficient
ratio was 2.6.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 800,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 60/40/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, 5 parts
by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator, and 2 parts by weight of
polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRY
CO., LTD.) were added together with 650 parts by weight of toluene,
and the mixture was uniformly dissolved and stirred, and the
acrylic adhesive solution (1) was prepared.
On one side of the polystyrene sheet, the manufactured protective
sheet was adhered by a roll laminator, and a polystyrene sheet with
protective sheet was fabricated.
On an XY stage mounting an adsorption plate of glass epoxy resin,
the polystyrene sheet with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of polystyrene sheet with
protective sheet in a diameter of 25 .mu.m by f.theta. lens, and
the surface was scanned by laser beam at a speed of 20 mm/sec by
galvano scanner, and was cut off. At this time, cutting of
protective sheet and polystyrene sheet was confirmed. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the polystyrene sheet (the
laser beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Comparative Example 1
The polystyrene sheet was processed by laser in the same manner as
in Example 1, except that protective sheet was not glued to one
side of the polystyrene sheet. When the processing area of the
laser beam incident side of the polystyrene sheet was observed,
sticking of much residue of scattering decomposition products was
recognized.
Comparative Example 2
The polystyrene sheet was processed by laser in the same manner as
in Example 1, except that ethylene-vinyl acetate copolymer sheet
(thickness: 100 .mu.m, extinction coefficient: 19 cm.sup.-1) was
used as base material of protective sheet. The extinction
coefficient ratio was 0.4. As a result, the protective sheet was
not cut off, and the polystyrene sheet in the lower layer was
processed by laser, and foams including decomposition product
residue were generated between the protective sheet and polystyrene
sheet. The protective sheet was irradiated with ultraviolet rays,
and the adhesive layer was cured. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
polystyrene sheet was observed, and sticking of much residue of
decomposition products of silicon wafer was recognized.
Example 2
The workpiece was a silicon wafer (thickness: 100 .mu.m). The
silicon wafer with protective sheet was manufactured in the same
manner as in Example 1, except that a silicone rubber sheet
(thickness: 25 .mu.m, extinction coefficient: 20.7 cm.sup.-1) was
used as base material of protective sheet.
Further, on a base material (thickness: 100 .mu.m) of polyethylene,
the acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness: 10 .mu.m), and an adhesive sheet was
manufactured. The adhesive sheet was glued to the back side of the
silicon wafer with protective sheet, and the silicon wafer with
protective and adhesive sheets was manufactured. By cutting in the
same manner as in Example 1, the protective sheet and silicon wafer
were cut off, but the adhesive sheet was not cut off. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the silicon wafer (the laser
beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that a
polyethylene terephthalate sheet (thickness: 25 .mu.m, extinction
coefficient: 80 cm.sup.-1) was used as base material of protective
sheet. By cutting in the same manner as in Example 1, the
protective sheet and silicon wafer were cut off, but the adhesive
sheet was not cut off. The protective sheet was irradiated with
ultraviolet ray, and the adhesive layer was cured. After peeling
off the protective sheet, the protective sheet gluing surface of
the silicon wafer (the laser beam incident side) was observed
particularly in the laser processing area, and decomposition
products (deposits) were not observed.
Comparative Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that
ethylene-vinyl acetate copolymer sheet (thickness: 100 .mu.m,
extinction coefficient: 19 cm.sup.-1) was used as base material of
protective sheet.
By cutting in the same manner as in Example 1, the protective sheet
was not cut off, but the silicon wafer in the lower layer was
processed by laser, and foams including decomposition product
residue were generated between the protective sheet and silicon
wafer. The protective sheet was irradiated with ultraviolet rays,
and the adhesive layer was cured. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
silicon wafer was observed, and sticking of much residue of
decomposition products of silicon wafer was recognized.
As known from these examples and comparisons, by using the
protective sheet of which extinction coefficient ratio is 1 or
more, contamination of surface of workpiece by decomposition
products can be effectively suppressed. Further, when processing a
metal material, by using the protective sheet having a base
material of which extinction coefficient is 20 cm.sup.-1 or more,
contamination of surface of metal material by decomposition
products can be effectively suppressed. As a result, the
decomposition product removing process can be substantially
simplified, and it contributes not only to reduction of
environmental impact but also to enhancement of productivity.
(Fifth and Sixth Aspects of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
[Measurement of Density]
The density of the base material of protective sheet and workpiece
was measured by using pycnometer and water.
Example 1
The workpiece was a polycarbonate sheet (thickness: 100 .mu.m,
density: 1.20 g/cm.sup.3). On a base material made of polyethylene
naphthalate (thickness: 20 .mu.m, density: 1.36 g/cm.sup.3), so
that the density ratio may be 1 or more, ultraviolet curable
acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness 10 .mu.m), and a protective sheet was
obtained. The density ratio was 1.13.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 700,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 65/35/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, 5 parts
by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator, and 2 parts by weight of
polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRY
CO., LTD.) were added together with 650 parts by weight of toluene,
and the mixture was uniformly dissolved and stirred, and the
acrylic adhesive solution (1) was prepared.
On one side of the polycarbonate sheet, the manufactured protective
sheet was adhered by a roll laminator, and a polycarbonate sheet
with protective sheet was fabricated.
On an XY stage mounting an adsorption plate of glass epoxy resin,
the polycarbonate sheet with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of polycarbonate sheet
with protective sheet in a diameter of 25 .mu.m by f.theta. lens,
and the surface was scanned by laser beam at a speed of 20 mm/sec
by galvano scanner, and was cut off. At this time, cutting of
protective sheet and polycarbonate sheet was confirmed. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the polycarbonate sheet (the
laser beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Comparative Example 1
The polycarbonate sheet was processed by laser in the same manner
as in Example 1, except that protective sheet was not glued to one
side of the polycarbonate sheet. When the processing area of the
laser beam incident side of the polycarbonate sheet was observed,
sticking of much residue of scattering decomposition products was
recognized.
Comparative Example 2
The polycarbonate sheet was processed by laser in the same manner
as in Example 1, except that polynorbornene sheet (thickness: 100
.mu.m, density: 1.00 g/cm.sup.3) was used as base material of
protective sheet. The density ratio was 0.83.
As a result, the protective sheet was not cut off, and the
polycarbonate sheet in the lower layer was processed by laser, and
foams including decomposition product residue were generated
between the protective sheet and polycarbonate sheet. The
protective sheet was irradiated with ultraviolet rays, and the
adhesive layer was cured. By peeling off the protective sheet, the
opening area of the laser beam incident side of the polystyrene
sheet was observed, and sticking of much residue of decomposition
products of silicon wafer was recognized.
Example 2
The workpiece was a polystyrene sheet (thickness: 100 .mu.m,
density: 1.04 g/cm.sup.3). The polystyrene sheet with protective
sheet was manufactured in the same manner as in Example 1, except
that a polyimide sheet (thickness: 20 .mu.m, density: 1.5
g/cm.sup.3) was used as base material of protective sheet. The
density ratio was 1.44. Further, on a base material (thickness: 75
.mu.m) of vinyl alcohol, the acrylic adhesive solution (1) was
applied, and dried to form an adhesive layer (thickness: 10 .mu.m),
and an adhesive sheet was manufactured. The adhesive sheet was
glued to the back side of the polystyrene sheet with protective
sheet, and the polystyrene sheet with protective and adhesive
sheets was manufactured. By cutting in the same manner as in
Example 1, the protective sheet and polystyrene sheet were cut off,
but the adhesive sheet was not cut off. The protective sheet was
irradiated with ultraviolet ray, and the adhesive layer was cured.
After peeling off the protective sheet, the protective sheet gluing
surface of the polystyrene sheet (the laser beam incident side) was
observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that a
silicon wafer (thickness: 100 .mu.m) was used instead of
polystyrene sheet. By cutting in the same manner as in Example 1,
the protective sheet and silicon wafer were cut off, but the
adhesive sheet was not cut off. The protective sheet was irradiated
with ultraviolet ray, and the adhesive layer was cured. After
peeling off the protective sheet, the protective sheet gluing
surface of the silicon wafer (the laser beam incident side) was
observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Comparative Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 3, except that
polynorbornene sheet (thickness: 100 .mu.m, density: 1.00
g/cm.sup.3) was used as base material of protective sheet.
By cutting in the same manner as in Example 1, the protective sheet
was not cut off, but the silicon wafer in the lower layer was
processed by laser, and foams including decomposition product
residue were generated between the protective sheet and silicon
wafer. The protective sheet was irradiated with ultraviolet rays,
and the adhesive layer was cured. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
silicon wafer was observed, and sticking of much residue of
decomposition products of silicon wafer was recognized.
As known from these examples and comparisons, by using the
protective sheet of which density ratio is 1 or more, or by using
the protective sheet having a base material of which density is 1.1
g/cm.sup.3 or more, contamination of surface of workpiece by
decomposition products can be effectively suppressed. Further, the
decomposition product removing process can be substantially
simplified, and it contributes not only to reduction of
environmental impact but also to enhancement of productivity.
(Seventh and Eighth Aspects of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
[Measurement of Tensile Strength]
The tensile strength of protective film and workpiece was measured
by using tensiron (Shimadzu Autograph AGS50-D). The measuring
condition is as follows.
Pulling speed: 20 mm/min
Chuck interval: 100 mm
Sample width: 10 mm
Example 1
The workpiece was a polystyrene sheet (thickness: 100 .mu.m,
tensile strength: 44 MPa). On a base material made of polyethylene
naphthalate (thickness: 50 .mu.m), ultraviolet curable acrylic
adhesive solution (1) was applied, and dried to form an adhesive
layer (thickness 10 .mu.m), and a protective sheet (tensile
strength: 282 MPa) was obtained. The tensile strength ratio was
6.4.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 700,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 65/35/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, 5 parts
by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator, and 2 parts by weight of
polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRY
CO., LTD.) were added together with 650 parts by weight of toluene,
and the mixture was uniformly dissolved and stirred, and the
acrylic adhesive solution (1) was prepared.
On one side of the polystyrene sheet, the manufactured protective
sheet was adhered by a roll laminator, and a polystyrene sheet with
protective sheet was fabricated.
On an XY stage mounting an adsorption plate of glass epoxy resin,
the polystyrene sheet with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of polystyrene sheet with
protective sheet in a diameter of 25 .mu.m by f.theta. lens, and
the surface was scanned by laser beam at a speed of 20 mm/sec by
galvano scanner, and was cut off. At this time, cutting of
protective sheet and polystyrene sheet was confirmed. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the polystyrene sheet (the
laser beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Comparative Example 1
The polystyrene sheet was processed by laser in the same manner as
in Example 1, except that protective sheet was not glued to one
side of the polystyrene sheet. When the processing area of the
laser beam incident side of the polystyrene sheet was observed,
sticking of much residue of scattering decomposition products was
recognized.
Comparative Example 2
The polystyrene sheet was processed by laser in the same manner as
in Example 1, except that ethylene-vinyl acetate copolymer sheet
(thickness: 100 .mu.m) was used as base material of protective
sheet. The tensile strength of the protective sheet was 17 MPa and
the tensile strength ratio was 0.4. As a result, the protective
sheet was not cut off, and the polystyrene sheet in the lower layer
was processed by laser, and foams including decomposition product
residue were generated between the protective sheet and polystyrene
sheet. The protective sheet was irradiated with ultraviolet rays,
and the adhesive layer was cured. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
polystyrene sheet was observed, and sticking of much residue of
decomposition products of polystyrene was recognized.
Example 2
The workpiece was a silicon wafer (thickness: 100 .mu.m). The
silicon wafer with protective sheet was manufactured in the same
manner as in Example 1, except that a polyimide sheet (thickness:
25 .mu.m) was used as base material of protective sheet. The
tensile strength of the protective film was 340 MPa.
Further, on a base material (thickness: 100 .mu.m) of polyethylene,
the acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness: 10 .mu.m), and an adhesive sheet was
manufactured. The adhesive sheet was glued to the back side of the
silicon wafer with protective sheet, and the silicon wafer with
protective and adhesive sheets was manufactured. By cutting in the
same manner as in Example 1, the protective sheet and silicon wafer
were cut off, but the adhesive sheet was not cut off. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the silicon wafer (the laser
beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that a
polyethylene terephthalate sheet (thickness: 25 .mu.m) was used as
base material of protective sheet. The tensile strength of the
protective sheet was 140 MPa. By cutting in the same manner as in
Example 1, the protective sheet and silicon wafer were cut off, but
the adhesive sheet was not cut off. The protective sheet was
irradiated with ultraviolet ray, and the adhesive layer was cured.
After peeling off the protective sheet, the protective sheet gluing
surface of the silicon wafer (the laser beam incident side) was
observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Comparative Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that
ethylene-vinyl acetate copolymer sheet (thickness: 100 .mu.m) was
used as base material of protective sheet. The tensile strength of
the protective sheet was 17 MPa. By cutting in the same manner as
in Example 1, the protective sheet was not cut off, but the silicon
wafer in the lower layer was processed by laser, and foams
including decomposition product residue were generated between the
protective sheet and silicon wafer. The protective sheet was
irradiated with ultraviolet rays, and the adhesive layer was cured.
By peeling off the protective sheet, the opening area of the laser
beam incident side of the silicon wafer was observed, and sticking
of much residue of decomposition products of silicon wafer was
recognized.
As known from these examples and comparisons, by selecting and
using the protective sheet of which tensile strength ratio is 1 or
more (the protective sheet of which tensile strength is 100 MPa or
more), contamination of surface of workpiece (or metal material) by
decomposition products can be effectively suppressed. Further, the
decomposition product removing process can be substantially
simplified, and it contributes not only to reduction of
environmental impact but also to enhancement of productivity.
(Ninth Aspect of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
[Measurement of Specific Heat]
The specific heat of base material of protective sheet and
workpiece was measured by using a heat analysis system (DSC EXSTAR
6000 of Seiko Instruments Inc.). Measuring at temperature rise
speed of 10.degree. C./min, three DSC curves of empty container,
sample, and reference (water) were determined. The specific heat
was calculated in the following formula.
Cps=(Ys/Yr).times.(Mr/Ms).times.Cpr where
Cps: specific heat of sample
Cpr: specific heat of reference (water: 4.2 J/(gK))
Ys: DSC curve difference of sample and empty container
Yr: DSC curve difference of reference and empty container
Ms: mass of sample
Mr: mass of reference
Example 1
The workpiece was a polyimide sheet (thickness: 100 .mu.m, specific
heat: 1.1 J/(gK)). On a base material made of polyethylene
naphthalate (thickness: 50 .mu.m, specific heat: 0.75 J/(gK)),
ultraviolet curable acrylic adhesive solution (1) was applied, and
dried to form an adhesive layer (thickness 10 .mu.m), and a
protective sheet was obtained in order that the specific heat ratio
may be less than 1. The specific heat ratio was 0.68.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 700,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 65/35/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, 5 parts
by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator, and 2 parts by weight of
polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRY
CO., LTD.) were added together with 650 parts by weight of toluene,
and the mixture was uniformly dissolved and stirred, and the
acrylic adhesive solution (1) was prepared.
On one side of the polyimide sheet, the manufactured protective
sheet was adhered by a roll laminator, and a polyimide sheet with
protective sheet was fabricated.
On an XY stage mounting an adsorption plate of glass epoxy resin,
the polyimide sheet with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of polyimide sheet with
protective sheet in a diameter of 25 .mu.m by f.theta. lens, and
the surface was scanned by laser beam at a speed of 20 mm/sec by
galvano scanner, and was cut off. At this time, cutting of
protective sheet and polyimide sheet was confirmed. The protective
sheet was irradiated with ultraviolet ray, and the adhesive layer
was cured. After peeling off the protective sheet, the protective
sheet gluing surface of the polyimide sheet (the laser beam
incident side) was observed particularly in the laser processing
area, and decomposition products (deposits) were not observed.
Comparative Example 1
The polyimide sheet was processed by laser in the same manner as in
Example 1, except that protective sheet was not glued to one side
of the polyimide sheet. When the processing area of the laser beam
incident side of the polyimide sheet was observed, sticking of much
residue of scattering decomposition products was recognized.
Comparative Example 2
The polyimide sheet was processed by laser in the same manner as in
Example 1, except that ethylene-vinyl acetate copolymer sheet
(thickness: 100 .mu.m, specific heat: 2.2 J/(gK)) was used as base
material of protective sheet. The specific heat ratio was 2.0.
As a result, the protective sheet was not cut off, and the
polyimide sheet in the lower layer was processed by laser, and
foams including decomposition product residue were generated
between the protective sheet and polyimide sheet. The protective
sheet was irradiated with ultraviolet rays, and the adhesive layer
was cured. By peeling off the protective sheet, the opening area of
the laser beam incident side of the polyimide sheet was observed,
and sticking of much residue of decomposition products of polyimide
was recognized.
Example 2
The workpiece was a silicon wafer (thickness: 100 .mu.m, specific
heat: 0.77 J/(gK)), and the silicon wafer with protective sheet was
manufactured in the same manner as in Example 1. The specific heat
ratio was 0.97.
Further, on a base material (thickness: 100 .mu.m) of polyethylene,
the acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness: 10 .mu.m), and an adhesive sheet was
manufactured. The adhesive sheet was glued to the back side of the
silicon wafer with protective sheet, and the silicon wafer with
protective and adhesive sheets was manufactured. By cutting in the
same manner as in Example 1, the protective sheet and silicon wafer
were cut off, but the adhesive sheet was not cut off. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the silicon wafer (the laser
beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that a
polyurethane sheet (thickness: 25 .mu.m, specific heat: 0.48
J/(gK)) was used as base material of protective sheet in order that
the specific heat ratio may be less than 1. The specific heat ratio
was 0.62. By cutting in the same manner as in Example 1, the
protective sheet and silicon wafer were cut off, but the adhesive
sheet was not cut off. The protective sheet was irradiated with
ultraviolet ray, and the adhesive layer was cured. After peeling
off the protective sheet, the protective sheet gluing surface of
the silicon wafer (the laser beam incident side) was observed
particularly in the laser processing area, and decomposition
products (deposits) were not observed.
As known from these examples and comparisons, by using the
protective sheet of which specific heat ratio is less than 1,
contamination of surface of workpiece by decomposition products can
be effectively suppressed. Further, the decomposition product
removing process can be substantially simplified, and it
contributes not only to reduction of environmental impact but also
to enhancement of productivity.
(Tenth and Eleventh Aspects of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
[Measurement of Refractive Index]
The refractive index of base material and organic workpiece was
measured by using Abbe refractometer (DR-M4 of ATAGO). The
measuring wavelength is 546 nm.
Example 1
The workpiece was a polypropylene sheet (thickness: 60 .mu.m,
refractive index: 1.51). On a base material made of polystyrene
(thickness: 20 .mu.m, refractive index: 1.59), ultraviolet curable
acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness 10 .mu.m), and a protective sheet was
obtained. The refractive index ratio was 1.05.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 800,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 60/40/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, 5 parts
by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator, and 2 parts by weight of
polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRY
CO., LTD.) were added together with 650 parts by weight of toluene,
and the mixture was uniformly dissolved and stirred, and the
acrylic adhesive solution (1) was prepared.
On one side of the polypropylene sheet, the manufactured protective
sheet was adhered by a roll laminator, and a polypropylene sheet
with protective sheet was fabricated.
On an XY stage mounting an adsorption plate of glass epoxy resin,
the polypropylene sheet with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of polypropylene sheet
with protective sheet in a diameter of 25 .mu.m by f.theta. lens,
and the surface was scanned by laser beam at a speed of 20 mm/sec
by galvano scanner, and was cut off. At this time, cutting of
protective sheet and polypropylene sheet was confirmed. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the polypropylene sheet (the
laser beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Comparative Example 1
The polypropylene sheet was processed by laser in the same manner
as in Example 1, except that protective sheet was not glued to one
side of the polypropylene sheet. When the processing area of the
laser beam incident side of the polypropylene sheet was observed,
sticking of much residue of scattering decomposition products was
recognized.
Comparative Example 2
The polypropylene sheet was processed by laser in the same manner
as in Example 1, except that polymethyl pentene sheet (thickness:
100 .mu.m, refractive index: 1.46) was used as base material of
protective sheet. The refractive index ratio was 0.97. As a result,
the protective sheet was not cut off, and the polypropylene sheet
in the lower layer was processed by laser, and foams including
decomposition product residue were generated between the protective
sheet and polypropylene sheet. The protective sheet was irradiated
with ultraviolet rays, and the adhesive layer was cured. By peeling
off the protective sheet, the opening area of the laser beam
incident side of the polypropylene sheet was observed, and sticking
of much residue of decomposition products of polypropylene was
recognized.
Example 2
The workpiece was a polycarbonate sheet (thickness: 100 .mu.m,
refractive index: 1.59). The polycarbonate sheet with protective
sheet was manufactured in the same manner as in Example 1, except
that a polyethylene terephthalate sheet (thickness: 20 .mu.m,
refractive index: 1.66) was used as base material of protective
sheet. The refractive index ratio was 1.04.
Further, on a base material (thickness: 100 .mu.m) of polyethylene,
the acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness: 10 .mu.m), and an adhesive sheet was
manufactured. The adhesive sheet was glued to the back side of the
polycarbonate sheet with protective sheet, and the polycarbonate
sheet with protective and adhesive sheets was manufactured. By
cutting in the same manner as in Example 1, the protective sheet
and polycarbonate sheet were cut off, but the adhesive sheet was
not cut off. The protective sheet was irradiated with ultraviolet
ray, and the adhesive layer was cured. After peeling off the
protective sheet, the protective sheet gluing surface of the
polycarbonate sheet (the laser beam incident side) was observed
particularly in the laser processing area, and decomposition
products (deposits) were not observed.
Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that a
silicon wafer (thickness: 100 .mu.m) was used instead of the
polycarbonate sheet. By cutting in the same manner as in Example 1,
the protective sheet and silicon wafer were cut off, but the
adhesive sheet was not cut off. The protective sheet was irradiated
with ultraviolet ray, and the adhesive layer was cured. After
peeling off the protective sheet, the protective sheet gluing
surface of the silicon wafer (the laser beam incident side) was
observed particularly in the laser processing area, and
decomposition products (deposits) were not observed.
Comparative Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 3, except that
polypropylene sheet (thickness: 60 .mu.m, refractive index: 1.51)
was used as base material of protective sheet. By cutting in the
same manner as in Example 1, the protective sheet was not cut off,
but the silicon wafer in the lower layer was processed by laser,
and foams including decomposition product residue were generated
between the protective sheet and silicon wafer. The protective
sheet was irradiated with ultraviolet rays, and the adhesive layer
was cured. By peeling off the protective sheet, the opening area of
the laser beam incident side of the silicon wafer was observed, and
sticking of much residue of decomposition products of silicon wafer
was recognized.
As known from these examples and comparisons, by using the
protective sheet of which refractive index ratio is 1 or more, or
the protective sheet having a base material of which refractive
index at wavelength 546 nm of 1.53 or more, contamination of
surface of workpiece (or metal material) by decomposition products
can be effectively suppressed. Further, the decomposition product
removing process can be substantially simplified, and it
contributes not only to reduction of environmental impact but also
to enhancement of productivity.
(Twelfth and Thirteenth Aspects of the Invention)
[Measurement of Number-Average Molecular Weight]
Measured in the same manner as in the first aspect of the
invention.
Example 1
The workpiece was a polycarbonate sheet (thickness: 100 .mu.m,
total coupling energy B: 720 kJ/mol).
On a base material made of polyethylene naphthalate (thickness: 50
.mu.m, total coupling energy A: 692 kJ/mol), in order that the
total coupling energy ratio may be less than 1, ultraviolet curable
acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness 10 .mu.m), and a protective sheet was
obtained. The total coupling energy ratio was 0.96.
The acrylic adhesive solution (1) was prepared as follows. In 100
parts by weight of acrylic polymer of number-average molecular
weight of 700,000 obtained by copolymerization of butyl acrylate,
ethyl acrylate, 2-hydroxy ethyl acrylate, and acrylic acid at ratio
by weight of 65/35/4/1, 90 parts by weight of dipenta erythritol
monohydroxy penta acrylate as photopolymerizable compound, 5 parts
by weight of benzyl dimethyl ketal (Irgacure 651) as
photopolymerization initiator, and 2 parts by weight of
polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRY
CO., LTD.) were added together with 650 parts by weight of toluene,
and the mixture was uniformly dissolved and stirred, and the
acrylic adhesive solution (1) was prepared.
On one side of the polycarbonate sheet, the manufactured protective
sheet was adhered by a roll laminator, and a polycarbonate sheet
with protective sheet was fabricated.
On an XY stage mounting an adsorption plate of glass epoxy resin,
the polycarbonate sheet with protective sheet was placed with the
protective sheet upside. Using YAG laser of wavelength 355 nm,
average output 5 W and repetition frequency 30 kHz, third harmonic
wave (355 nm) was focused on the surface of polycarbonate sheet
with protective sheet in a diameter of 25 .mu.m by f.theta. lens,
and the surface was scanned by laser beam at a speed of 20 mm/sec
by galvano scanner, and was cut off. At this time, cutting of
protective sheet and polycarbonate sheet was confirmed. The
protective sheet was irradiated with ultraviolet ray, and the
adhesive layer was cured. After peeling off the protective sheet,
the protective sheet gluing surface of the polycarbonate sheet (the
laser beam incident side) was observed particularly in the laser
processing area, and decomposition products (deposits) were not
observed.
Comparative Example 1
The polycarbonate sheet was processed by laser in the same manner
as in Example 1, except that protective sheet was not glued to one
side of the polycarbonate sheet. When the processing area of the
laser beam incident side of the polycarbonate sheet was observed,
sticking of much residue of scattering decomposition products was
recognized.
Comparative Example 2
The polycarbonate sheet was processed by laser in the same manner
as in Example 1, except that ethylene-vinyl acetate copolymer sheet
(thickness: 100 .mu.m, total coupling energy A: 962 kJ/mol) was
used as base material of protective sheet. The total coupling
energy ratio was 1.34. As a result, the protective sheet was not
cut off, and the polycarbonate sheet in the lower layer was
processed by laser, and foams including decomposition product
residue were generated between the protective sheet and
polycarbonate sheet. The protective sheet was irradiated with
ultraviolet rays, and the adhesive layer was cured. By peeling off
the protective sheet, the opening area of the laser beam incident
side of the polycarbonate sheet was observed, and sticking of much
residue of decomposition products of polycarbonate was
recognized.
Example 2
The silicon wafer with protective sheet was manufactured in the
same manner as in Example 1, except the workpiece was a silicon
wafer (thickness: 100 .mu.m).
Further, on a base material (thickness: 100 .mu.m) of polyethylene,
the acrylic adhesive solution (1) was applied, and dried to form an
adhesive layer (thickness: 10 .mu.m), and an adhesive sheet was
manufactured. The adhesive sheet was glued to the back side of the
silicon wafer with protective sheet, and the silicon wafer with
protective and adhesive sheets was manufactured.
By cutting in the same manner as in Example 1, the protective sheet
and silicon wafer were cut off, but the adhesive sheet was not cut
off. The protective sheet was irradiated with ultraviolet ray, and
the adhesive layer was cured. After peeling off the protective
sheet, the protective sheet gluing surface of the silicon wafer
(the laser beam incident side) was observed particularly in the
laser processing area, and decomposition products (deposits) were
not observed.
Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that a
polyethylene terephthalate sheet (thickness: 25 .mu.m, total
coupling energy A: 692 kJ/mol) was used as base material of
protective sheet.
By cutting in the same manner as in Example 1, the protective sheet
and silicon wafer were cut off, but the adhesive sheet was not cut
off. The protective sheet was irradiated with ultraviolet ray, and
the adhesive layer was cured. After peeling off the protective
sheet, the protective sheet gluing surface of the silicon wafer
(the laser beam incident side) was observed particularly in the
laser processing area, and decomposition products (deposits) were
not observed.
Comparative Example 3
A silicon wafer with protective and adhesive sheets was
manufactured in the same manner as in Example 2, except that
ethylene-vinyl acetate copolymer sheet (thickness: 100 .mu.m, total
coupling energy A: 962 kJ/mol) was used as base material of
protective sheet.
By cutting in the same manner as in Example 1, the protective sheet
was not cut off, but the silicon wafer in the lower layer was
processed by laser, and foams including decomposition product
residue were generated between the protective sheet and silicon
wafer. The protective sheet was irradiated with ultraviolet rays,
and the adhesive layer was cured. By peeling off the protective
sheet, the opening area of the laser beam incident side of the
silicon wafer was observed, and sticking of much residue of
decomposition products of silicon wafer was recognized.
As known from these examples and comparisons, by selecting and
using the protective sheet of which total coupling energy ratio is
less than 1, or the protective sheet having a base material of
which total coupling energy A is less than 800 kJ/mol,
contamination of surface of workpiece by decomposition products can
be effectively suppressed. Further, the decomposition product
removing process can be substantially simplified, and it
contributes not only to reduction of environmental impact but also
to enhancement of productivity.
INDUSTRIAL APPLICABILITY
The protective sheet for laser processing of the invention is used
when processing the workpiece by ultraviolet absorption ablation of
laser beam. The invention also relates to the manufacturing method
of laser processed parts obtained by processing of workpiece, such
as cutting, drilling, marking, grooving, scribing, trimming and
other processing, by ultraviolet absorption ablation of laser
beam.
* * * * *